The words "Porsche" and "Cheap" or "Reasonable" never seem to appear together very often. One of the options to have on a 993 are "Sport Seats" which have hardbacks, they command $5k to $10k a pair here, a well known vendor in Europe has some new OEM's for sale, only $20k:
Factory Sport Seats - Carnewal
If you want "Cheap" power, buy anything with a GM LS motor in it.