if you are talking about time building and buy a block of hours, yes, usually their quotes are correct, and u may be able to get a discount, if you buy 10 hours or more.
about conversion from a JAR to FAA. you shouldn't have any problems as these license are all ICAO.So the FAA should give you a temporary license the same day.
You just need a new FAA medical which usually cost around 60-80$ and good for 2-3 years. You must obtain a "release form" from your CAA, for 40 pounds to get a FAA privat license.