Train travel to Barcelona

I wasn't aware that there was that much difference in the promo prices when tickets first go on sale.

What is your origin point for the trip?

It appears from renfe.com that promo prices for April have not been loaded yet.

Why are you looking at RailEurope instead of the national train site?

http://www.renfe.com/EN/viajeros/index.html

I am going from Paris to Barcelona on May 8th ( tuesday) and in the past few month I have been entering the most current date that was available (120 days prior) to get a idea of what the tickets would cost. They were always under $80 USD however today when I did it the April prices were $150 USD for the same train 2nd class. I just wondered if I should wait , or buy them when the date opens up if it is $150? seems high?

Thanks for any and all advice given, I am new to this. Which site is easiest to use?

Use Trainine.eu or http://www.sncf.com/en/passengers. Ticket prices do not usually go down once they have been released. Note that prices also may fluctuate seasonally so if there is usually a lot of demand in May or even on the date that you plan to travel, the prices will be higher -- it is supply and demand.
Edit: May has a number of French holidays so there may be expectation of a lot of demand that month and specifically May 8th is a holiday with one also on the 10th so that may explain the higher prices as people travel for the holidays.

Definitely trainline.eu for ease of use and good pricing. Had I known you are starting in Paris I would not have suggested Renfe ( it is notoriously quirky but the best place for train tix entirely within Spain).

Easter is Sunday, April 1st, schools around Europe are on vacation for a couple of weeks. Prices will go up. So as others have said, use another web seller but get ready to pounce the day tixs go on sale.

The French rail system has been rebranded: https://en.oui.sncf/en/
I have bought its tickets for many years with no difficulty and it is certainly easier to use now than a couple of decades ago. However, forums such as this one have in the past reported some US customers having difficulties with their credit cards.

In general, RailEurope is the least efficient source of info and tickets.

As Lola mentioned, the set of discounted tickets can be added into Renfe's database a day or two after the regular, full fares. It's not a one-step process on the back end of the web site and everything is not always right on-time 120 days out. It's possible that the deepest discounts will not be offered for peak travel times around Easter, but some should be.

Rail Europe's prices can be a few dollars higher than Renfe's, but they are drawing them from the same database. Fairly easy to see that, but at the same time, you probably don't know exactly the exchange rates and fees that your credit card will apply to a foreign transaction.

Just checked OUI - newly branded SNCF site
Tickets into mid April - after Easter weekend are running from a low of 39E to high 89E - with many days at 49 and 59E.
If you contact the train company they will email you when tickets come up for sale.

Well, you can fly for $39.
Flight is 1 hour 50 minutes.
And you can buy the tickets now.

Air is cheap but you have to pay for transfers to the airport, baggage, seats, etc
train is better as I am staying near the train station