I think hour building in the UK and hour building in the US are flown differently. When I say that I mean that if you booked 100hrs in the UK you would probably fly it off over several weeks/months and may just burn holes in the sky, retracing the same routes with the odd trip outside your usual boundaries.
If you went to US, you would be going with a mindset of yes flying hours off but also having a bloody good time whilst you are over there. I think this is demonstarted here as people are enquiring about where is interesting to go. If this is the case and you actually intend to do something with your time over there and not burn hours off then a few hundred pounds difference when you inc hotels, etc wont really make any difference to you.
It doesnt to me when I go over there, which I still do despite owning a share in a very nice IFR equipped aircraft over here.
I would also add that if you were hiring a C150 then I have no doubt that the cost difference these days is going to be minimal, if you were penny watching then you may in fact end up staying this side of the Atlantic if that is all you wanted to do. However, when I go Stateside and go touring I prefer something a bit nicer than a C152 with bits hanging off it, last time I hired a brand new C172 SP with G1000 for $150/hr WET. When you venture into nice twins then the cost differential is even greater - this is when going Stateside could be more beneficial to you.
J.