I'm in London and i'm not sure that UK Elises will work out all that cheaper...
Auto Trader UK - LOTUS ELISE 111S 2dr Convertible (not sure if link will open in US. let me know if it doesn't)
Here's an ad for the cheapest 111 I could find ('03, 48k miles and £10k) and by the time you add shipping and currency exchange you're close to $17k.(and the steering wheel is on the wrong side). Didn't someone on here buy an 05 for under $20k?
(S1 Elises start at £5k for a high mileage '96 tho')!
As far as I can see (apart from the engine of course) they're identical bodywork wise.