I can't answer the licence conversion question, but I can help with aircraft cost.
In New Zealand expect anywhere between NZ$140 - $170 per hour (hobbs) for a C172 or Cherokee. Add an instructor for around $20/hr to $45/hr depending where you go.
You'd obviously pay a little less for a 2-seater (C152, Tomahawk between $120 and $150) and a little more for a complex single (arrow, C177, Mooney, C180, C182 - anywhere from $150 to $250 depending on the place and model).
As for the best place to go flying? New Zealand of course!! (not that I'm biased... :P) Flying around the southern alps (South Island) is incredible, but don't ignore the rest of the country as well.
If you want any more info, or web-sites to try give me a yell.
Good luck, fly safe.
Dupre.