A clutch replacement is not a casual maintenance task. With M20 engines, the two upper transmission to block bolts are especially difficult to access and remove.
I drive a 91 318i and paid $625 (parts and labor) to have the clutch, throw-out bearing, pressure plate, and rear transmission mounts replaced. You/they will also have to send your flywheel out to a machine shop for inspection and/or resurfacing.
Here's a link on an E36 318is clutch replacement how-to for a general idea on how extensive this procedure is Pelican Technical Article: BMW Clutch Replacement
Good luck with it.