You may be best off with a 3Ltr one. They were available '94 onwards, and standard ones may have been looked after better and not thrashed like a lot of the 2.5TT's. They have much better economy, and more standard engine parts (same as N/A Supra mk4).
The other option is the later turbo. Available late '96 onwards, they come with a single turbo and VVTI. More powerful and better economy than the earlier Twin Turbo's.
There are not many of either of those models around for sale in the UK though, so you may have to think about importing if you want a really pukka one!
A well looked after Soarer will go on for ages though, try and find one with service history, and you shouldn't have many problems.
Don't expect them to be 'cheap' to run though!
What would be better would be to buy a good low milage Soarer, and use the IS for travel:p
An early Twin Turbo can go for around £3,000, but its worth spending a bit more for a good one. Up to around £5,000 for <'94. '94 was a facelift year, so late '94/'95/'96 go for a bit more. Then '97 onwards pay around £7,000 ish at least for the single turbo.
3Ltr can go for a little more purely because there are not so many around. £6,000ish for a good pre'96, then again, £7,000+ for '97 onwards when there was another facelift for all Soarer's.
TTs and 3Ltrs didn't come with the touchscreen that came on the V8s. But '97 onwards there was an option for a built in screen which tilts to reveal the CD player. There are ways to add UK satnav to these. Expect to pay around a grand. Or just buy one of the handheld ones that stick on the windscreen.
Good luck!!