Carrera and Carrera 4 use the 3.4 litre M96. The Turbo arrives at the end of this window with the Mezger engine, which does not share the 3.4's reputation.
Prices are set mostly by mileage, records and colour. A well-documented higher-mileage car is usually the better buy over a cheap car with gaps.
The GT3 of this period is Europe-only in most cases, so US listings are rare and priced accordingly.