MattsClio, what difference does it makes that it is an import ? A huge number of people on these boards have import 172s and they came with a 3 year warranty anyway.
Do a search on the boards for warranty and you will find many threads on this subject explaining this topic.
As for alarms, you can get one for £250 at your local car alarm firm, that is what I did, so..... you can get a brand new 172 with alarm and warranty for £11,249 !
Up to you if you want to spend more than you need mate.