I have lived on Alscot Road for the last 2.5years. To be honest, I am not entirely sure what a fair price for a flat there is now given the events of the last couple of years & the current economical environment, but when I was buying 290k was approx the price of a 2-bed. You may want to check what the sales prices of some of the new developments along Spa Road & at St James have been to compare. Even check what prices they are asking at Bermondsey Square right now.
Regarding tubes from Alscot road; Bermondsey is definitely geographically closest (about 10mins walk) though the route does take you down Spa Road & under the bridge which I don't like to do on my own late at night, so I would rather go to Lon Bridge (20 mins walk) & taxi it or get off at Waterloo/Elephant & take the number 1 bus which drops you at Alscot Rd.
It depends on where you work etc. but personally I rarely take the tube anywhere anymore since moving to SE1. The 78 and 1 buses stop on Grange Road right next to Alscot. The 78 can have its issues with regularity but I find the 1 a very reliable route which takes you quickly to Elephant (tubes), Waterloo, Covent Garden (approx 20 mins)& Tottenham Court Road. It's also a night bus that goes every 30mins after 0.30. You can also get the 188 or 42 from Grange Road.
I have lived next to Spa park for a year and a half now, having moved from Borough (right next to Borough tube station). Although I miss being right next to the tube, I can honestly say I prefer the Spa area and the transport links are fine. It is a lovely quiet area and still close to restaurants/bars etc. of Bermondsey St, Shad Thames, London Bridge, Borough etc. Local amenities are great, a lovely new doctors surgery (in Artesian), Andrew Kirby vet for our dog, big tescos down Dunton Road etc.
Bermondsey tube station is definitely the closest and takes 10 minutes from Spa park. I am a bit hesitant about walking home from there in the dark at the moment (esp later in the evenings), but this is because most of the developments along there are not yet lived in and there is hardly anyone around. Once the developments fill up and there are more people I am sure I will have no qualms about walking from there at night.
I walk to London Bridge often too, it takes me about 15 mins (20 for my hubby!).
We also use the buses (no 1 and no 78 buses) all the time, the bus network is great and something I really just discovered on moving here.
Sorry i can't comment on the prices but I would do my research on property sites and perhaps call around local real estate agents for their take on it.
2 bedroom flat means nothing really as some bedrooms are so small, what you want to compare is the square footage to other flats and make sure the layout is not terrible as people will be picky when you come to sell. Does it have parking? (extra 25k usually) and a view...over the park much better than over Grange road.
From memory the 'average' flat there was 285-325k off plan, with variations depending on view and floor level.
I think by 'The Spa', you mean 93 and 95 Alcot Road (opposite Artesian). I was a FTB when I bought a one-bed in that block in April of this year and think it was a good move for me. I'm not sure if you are interested in the one next door to me that is marketed at £300k, but it seems reasonable and comparable with other developments. The outside patio area backs onto the back of "The Fort" which is certainly an interesting neighbour but I have never had any problems from there. For the record, my dealings with the management company, Montalt, have all been amicable too.
I think that the bus routes are very handy. The 1 is a great service. Bang outside, every 10 minutes, usually plenty of space and the night bus service is equally valuable as it has saved me a lot on night time taxis from Soho and Waterloo, etc. The 78 is good for returning from Shoreditch but it is pretty miserable going towards the city. Actually, I would like to know how I can petition TFL to stick another few buses on that route as I have never seen it without anyone standing up. As commented above, 188 is also a useful bus route as Tower Bridge Road is just a short walk. For the underground, I'd echo other comments that the route from Bermondsey station is a little dingey, but I have never had any problems and when the top end (and middle) of Spa Road is finished - if it will ever be - then it will be fine. I've tended to walk to London Bridge, though, as the Jubilee has been shut almost every weekend this summer.