Honestly, it's not that hard. There's even write-ups on this site showing it step by step. The hardest part is getting the trans on/off the engine since it's a good amount of weight. But it's nothing a floor jack and coupe blocks of wood can't handle.
I'd say anywhere from the $150-$300 range, but to me $300 is pretty high for how easy it is to do a clutch in one of these cars.
1991 HF - previously '90 B18A1 now '97 B18C1
1989 Si - running parts car/gone