Best and reasonably priced can never be used in the same sentence in the turbo Buick world
There are several people that are capable of building you a short block. You need to be more specific with your goal. Stock short block? Will you race the car? How much HP ? Lots of variables. make sure you find a person that knows the turbo buick engines as the tolerances are much tighter than a small block Chevy. Good luck. Call your vendor and ask them. If you dont have a vendor I would suggest Jack Cotton.
Bryan