Bath to Stonehenge Inner Circle; tips on tickets and transportation

The train to Salisbury is easy enough - but then falls foul for these visits as the shuttle bus from the station doesn't generally service the early and late slots. So then it's a taxi - easy enough to get one there, a bit trickier (as in more expensive) to get one back

Not sure what you are meaning in the first part of your question - you don't need to be a member to book an inner circle tour and can book as many tickets as you want. in fact, membership only gives a £15 discount.

I don't know anything about this taxi company but have just found them on a google search, they claim to be Stonehenge specialists at £24 there, and £29 back.
https://www.your-taxi.co.uk/stonehenge
The last shuttle bus to Stonehenge leaves Salisbury Station at 4pm and Stonehenge at 7 pm. The one there may be OK, but clearly the one back is too early.
The train from Bath runs hourly at 35 minutes past the hour, taking 1 hour, returning at 42 minutes past the hour to 9.42 pm, then a last train at 11pm

Thank you jgdh and isn31c, this is helpful.

In regards to the membership, it appears that only 1 regular ticket is available for the 6:45 pm inner circle experience. What I was able to see in the booking section is that there is also 1 ticket available for members. My thought was to purchase 1 membership so I would be able to obtain 2 needed tickets. Hoping that this makes sense and that I am actually able to do it. We are coming from US and want to book this soon but was concerned that I may be missing something and this is less expensive than the $811 quote for a private tour.

My other concern was the ability to get a taxi in Salisbury to and from Stonehenge. Do you think that it will be an issue getting a taxi at 8:00 pm back to Salisbury train station?
Thank you

It sounds like you can buy the 2 tickets you need if you buy a membership for the one. But I'd recommend telephoning English Heritage during their business hours to confirm this, especially because in the time since you posted this, one or both of those tickets might have sold. Customer Service is at 0370 333 1181 (Monday to Saturday).

Stonehenge is very much worth visiting, IMO, outside of the special inner circle hours. The visitor centre closes at 1700 (5 PM), according to the website. There is quite a lot to see there, with both outdoor and indoor exhibits, and it really helps you understand what you're looking at when you go out to the stones. Also, the inner circle doesn't have the audio guide which, again, really helps you understand what you're looking at.

https://www.english-heritage.org.uk/visit/places/stonehenge/things-to-do/visitor-centre/

If you do get those evening inner circle tickets, I'd encourage you to arrive a few hours early so you can benefit from the visitor centre and audio guide. There's a large book/gift shop and a nice cafeteria with many food choices, so you won't have to starve while waiting for your inner circle time. The only inconvenience will be having to wait outside -- probably in the car park -- which could be fairly miserable if it's raining.

During the regular visiting hours, there's a free shuttle minibus to & from the stones which you can take halfway and walk the rest, or walk the whole way, whatever you want. For the inner circle tours you're required to ride the minibus, and I believe your ticket warns that it won't wait if you're late; you'll simply miss your slot.