Interesting...
Is the cost the only issue tho?
Boston is a relatively big city, Cheltenham a smallish country town.
Would you move from say Boston to an 'equivalent' town in the US? Say Lincoln, Nebraska? If the answer to that is yes then you can add cost to the equation.
Cheltenham is a very genteel conservative country town. By and large well heeled (but with an increasing Chav issue) with a predominantly white middle class population. It does not necessarily have the diversity of cultural, leisure and entertainment facilites of a Boston...museums, theatres, restaurants etc.
If your idea of a good night out is to hit a good restaurnat and follow that up with a decent nightclub then you may be disappointed ( or have to go to London or B'Ham to do that, with its cost issues).
If however you want to be close to some decent drving roads and an hour of so from the Race track called 'Wales'
for a decent run in the P-car then that's good.. or you love horse racing.....
If you want a decent fairly quiet rural town lifestyle then Cheltenham's the place for you....the work will be different, the pace and style of life will be different...all of which in all honesty are more important factors than the 'cash' cost of living...
Sure food will be somewhat more expensive, as will gas, cars and housing....
Currently the $ to £ ratio is not good at all for you guys, seriously not...around 2:1...
If you are in a US company moving you to the UK then you would need to get a revision to your income/ benefits to enable you to enjoy an equivalent lifestyle...but this more to cover the increased cost of accommodation and income tax than basics.
Certainly if I were to move the other way the direct exchange in salary would afford me a greater disposable income than I currently enjoy, however I know that the current rate for an equivalent job over there is not that direct comaprison...so if I were to earn what they earn my lifestyle would be broadly similar; in addition the health care insurance cost would be proportionally far far great (something like a factor of 10.)
I think its more important to see what the type of life you would have if you moved there than its cost. It may be that no matter how much you earned living in Cheltenham just isn't your thing.
PM if you want to talk more......