Strange pricing for train from London to Liverpool

Where are you looking for prices, and what date are you using?

The National Rail website (nationalrail.co.uk) is the place to go for information and tickets. It currently isn't showing schedules for dates after February 15, so you must be seeing those strange prices from a third-party seller. Go to the National Rail website and use a date in the first half of February that matches the day of the week you want to travel. That will give you a very good idea of the pricing you can expect for your travel date when the time comes. For the random February day I chose, there were two trains much, much more expensive than the others. Their departure times were 9:30 AM and 5:30 PM--something related to long-distance commuters maybe?

I think it would be very unusual for a high-speed train to make two stops in the same city. One of the ways they are able to cover a distance so rapidly is that they don't make many stops. In the case of your trip, it appears the trains use London Euston and Liverpool Lime Street.

Look on the train operator’s website which is Avanti West Coast https://www.avantiwestcoast.co.uk/

Tickets are on sale for up to Feb 2022. Beyond that date, tickets are yet to go on sale. Prices vary due to ticket type – you need to look for Advance tickets. To get an idea of ticket prices look at dates in February. The top prices you see are for walk-up fares – which no one in their right mind buys for long-distance journeys.

Your starting point is London Euston ending in Liverpool Lime Street station. The fastest trains usually only stop at one station in a city/town. Where they stop will be shown in the timetable for a particular service. Look for direct trains with no changes.

There is really no need to book rail tickets long in advance, and timetables and fares for next spring have not yet been set. I think the difference in prices is that between direct trains and those requiring a change. The direct trains are in fact cheaper and faster, so there is litte point in choosing any other. They run twice each hour and take 2 hours 13 minutes, stopping at other stations on the way, but only at Lime Street station in Liverpool.

Advance tickets are restricted to a specific train on a particular day. Alternatively, you can buy an open ticket which lets you travel on any train, but then you cannot reserve a seat, which is always a good idea. Prices vary according to the time of day - more expensive at busier times. You have to decide your priority.

I don' t know where you are looking, but there are not departures every few minutes. There are a number of departures--without change--and the trips are a little over two hours.

Use the website acraven posted.

There can be a big difference between full fare “Anytime” prices and Off-Peak and Advance fares.

In the UK in general (I know nothing about the London-Liverpool route specifically), there's a risk attached to buying rail tickets very late. The UK has some of the highest per-mile walk-up fares in Europe. You can see that in action by pricing out some trips for today or tomorrow. It can get painful. Whether it is sometimes/usually/always adequate to buy tickets something like 2 weeks in advance, I do not know. I do know that a kind ticket agent talked turkey to me about this back in 2017 when I wanted to buy a current-day or next-day ticket. First, he helped me select a well-priced departure time, then he told me I should never wait so late again.

There are two companies operating this route
Avanti, which run the fast services.. (these are not high-speed) is unusual in that there are three classes on their trains. London North Western run slower services
Suggest you consult www.seat61.com for information on rail travel in UK including how to book tickets from abroad

The Man knows all, including a game called split ticketing

Depending how much travelling you are doing a discount pass like the TwoTogether likely will save you money.
I use national rail and then put results through the Split Tickering AP
On occasion the normal fare of £51 has been as low as £22 on a journey I do.
This is for being on exactly the same train

At the moment you are too early for Advance tickets tied to specific trains and are probably looking at anytime off-peak standard single tickets if you are only looking at a headline price per train. Returns may be cheaper if coming back to London.

For Avanti, the faster trains, there are three data points on returns. An eyewatering £342.60 for Anytime, and £94.50 for off-peak, which during the day is 09:27-15:00.

For the slower trains the corresponding rates are £129.30, and £47.25 after 8:45. Plus a cheaper point of £36.60 with more complex restrictions.

My advice is to set up an Advance ticket alert with Avant here, and look on the day when the Advances become available, as well as potentially utilise Railcard discounts and split ticketing as others have said.

A railcard costs £30 gives you a third off the price for a year. Even better still, a 2together railcard cost £30 and allows two a third discount, so long as you travel together. So if you are spending in excess of £90 on rail travel a railcard will save you money.
As others have said, travel from London Euston to Liverpool Lime Street. Avanti are fast, comfortable trains, standard class is perfectly acceptable. London North Western trains tend to be older, slower and make more stops.

Avantiwestcoast.co.uk

Long distance trains usually only stop in one station per city/town otherwise they wouldn't be high speed. An exception to this is the Avanti train into Edinburgh from England, where the train stops at Edinburgh Haymarket about 5 minutes before its terminus at Edinburgh Waverley, they're are about a mile apart, after a 400 mile journey from London.
If you take a short distance train, say Liverpool to Manchester, a 35 mile trip, there can be many stops in each city along the route between the city centres.

London North Western trains tend to be older, slower and make more stops.

Class 350 fully airconditioned Desiro trains are not especially old, nor are they particularly slow. Avanti can run at 125 mph, the 350s aren't far behind at 110 mph. As the commuter trains have to pick up and drop off the commuters, yes it does stop more often. But with judicious route knowledge and a change at the right time London Northwestern can get you from the northwest to London very inexpensively and quite quickly.