I don't have any local knowledge, but this is what I could find out online:
Season tickets
Indeed a 7-day season ticket costs £95.60 and gives you unlimited travel between the two stations for 7 consecutive days starting on any day of your choosing. So if you have any other travel in the area planned before or after then you might be able to use your season ticket for that as well.
If you want a paper season ticket, then you'll also need a photocard to go with it -
just bring a passport photo to a station and they'll make one for you for free (and you can buy the season ticket at the same time). The photocard will have an number/code on it that you must provide when buying season tickets, as it will be printed on the ticket, and the ticket is only valid when shown together with the photocard, to ensure that nobody else can use the ticket.
However, I can see that CrossCountry offers the option of getting your season ticket on a smartcard, and
according to the FAQs you don't need a photocard to go with it. You'll need to make an online account and then
order a smartcard to be sent to you for free using this link (allow a week for delivery). You can then
use this link to buy the season ticket for the smartcard online, and download it to your card using your phone, or you can still buy and/or download the ticket to your card at the station.
Return tickets
For the travel times you have indicated, you can actually use an Off-Peak Return ticket from Birmingham New Street to Cheltenham Spa for £28.30. As you can see on the
National Rail Enquiries Journey Planner, on weekdays, you can use this ticket to travel out on any train starting from the 09:30 departure, and you can return on any train starting from the 09:59 departure. If you're only going on Wed+Thu+Fri, then three return tickets work out at £84.90 which is cheaper than the season ticket. (Sometimes it's slightly cheaper to buy two Advance Single tickets instead of a return ticket, but those are only valid on the specific train selected so if you miss it then you'd have to buy a new ticket - I don't think using advances would be worth the saving in this case.)
Split tickets
It is possible to save more money using split tickets (i.e. buying two or more tickets that join together to cover your journey), but it's a bit more complicated as there are rules to be followed (see the
National Rail Conditions of Travel section 14), which are roughly:
* If the split is between two non-season tickets, then the train must stop at the station where your tickets split
* If the split is between two season tickets or between a season ticket and a non-season ticket, then the train must pass through the splitting station but does not have to stop. (It's not clear how well-versed staff are about this rule, and whether you might have to argue your case if inspected on a non-stopping train.)
Searching for a day return journey on
trainsplit.com yields a suggestion of splitting at Worcestershire Parkway. That would be £10.20 Off-Peak Day Return from Birmingham to Worcestershire Parkway, and a £9.00 Anytime Day Return from Worcestershire Parkway to Cheltenham Spa, for a total of £19.20 per day, or £57.60 for three days. However, you can only use these tickets on trains that stop at Worcestershire Parkway.
If you instead split weekly season tickets at Worcestershire Parkway, you get a cost of £36.80 + £42.70 = £79.50. This would allow you to travel also on trains that pass through Worcestershire Parkway without stopping. (
Can someone confirm if this is all direct trains from Birmingham New Street to Cheltenham Spa?) You can also buy a season ticket for one half and day returns for the other half, which for 3 days amounts to £36.80 + 3*£9.00 = £63.80, and allows travel on the same trains as the combination of two season tickets.
It might be possible to get a lower price by splitting at a different station - I haven't checked the alternatives.
Travel warnings
Finally, I note that searching the journey at nationalrail.co.uk yields two warnings:
* "Cheltenham Festival 15-18 March. [...] A queuing system may also be in place to enter or exit the station. Allow plenty of time to catch your train." You will probably want to ensure your tickets are valid on any train, so that you can just board the first one that turns up when you get to the front of the queue. (If the queueing system is based on which trains people are catching, then you should try to get reservations for your preferred train.)
* "Amended CrossCountry service until further notice [...] If you are travelling on days from Monday 21 February onwards, please check back closer towards your intended time of travel." This means that you don't know for sure which trains will run yet, so you probably don't commit to a particular plan of action. For example, you can order your smartcard for free now and/or get a photocard sorted if you prefer, but there's no benefit to buying season or return tickets this far in advance (except possibly if you want to get seat reservations), as their prices do not change with time and they cannot sell out.
