Funnily enough I don't think the US is cheaper for jet flying although you can simply rent, rather than need to find a friend with a jet.
In the UK find someone who owns a share in one and offer to fill the tanks for them in return for a flight. I know if I was checked out I'd happily take some cost sharers along, I hate flying alone, however the cost of becoming self authorising on a jet is significant.
The other option is to look at buying a share. Most reasonable groups will give a serious contender a flight before getting them to commit. Who knows you might like it and want to join. That is the point of a test drive.
Delta jets
www.deltajets.com will give you a ride in one of their hunters if you join the club for £1500 which when you consider the running costs of a hunter (£800ish) per hour seems a good deal.
If I was to commit some money to a jet flight I'd do it in something interesting like the hunter. A provost is fun for the novelty of needing to wear a helmet and gro bag and you sit on top of a live seat. A JP3 however is not fast, its noisy, but not inspiring.
Drop me a message if you want to discuss.