High cost?
Tranny, Engine, drive axles.
As far as looking for...
Make sure the Transmission shifts into gear from neutral well when the car is cool. Go thourgh every gear several time to see that they engage and don't have any syncro problems. Make sure to dirve it at least 30 miles and turn the car off half way through to see that no CEL's where cleared and then come back while driving. Look at the CV axles boots to make sure they are not torn or leaking, look over the engine and see if there are any noticable fluid leaks. Check the coolant resivior for Oil. Check the tire wear to make sure it's even. Look for any Transmission fluid leaks. Ask about an Extented warrenty or if it's from an individual take it to a mechanic and have them pay for the inspection.
Oh and best of luck.
