I'm originally from the UK and I would look at the Imperial War Museum, the British Museum or the Victoria and Albert Museum. The IWM is a MUST see.
Forget hotels; go with Bed and Breakfast places, lots of them in London and a fraction of pricey hotels. Google is going to be your friend and look for sites with actual reviews from real folks who have stayed there recently. Stonehenge is well, underwhelming unless you absolutely have to see it. I would stay in London and see the museums and visit the aforementioned high end gun shops. You can always visit Harrods and Fortnums and Masons (high end shopping) for the female unit. Don't forget the London Eye, Houses of Parliament, Tower of London, Buckingham Palace and well, a crap load of historical and cultural places.
DON'T get sucked in by con men selling all kinds of tourist crap, there are hundreds of 'em in London. Have a good time but seriously, pass on Stonehenge. If you want to get out of the city, go see Windsor Castle instead. It's a lot closer to London and there's a lot more to see.
Have some fish and chips for me as well as some English beer.... ;-)
