How much does it cost to replace a clutch in 2000 Toyota celica And should flywheel need replaced as well?

Obviously this would depend on who does the work, but I'll give you some basic facts from my own experience.

To replace my car's clutch at about 90k miles cost about $1,200. This included the flywheel - I believe it was reconditioned instead of outright replaced. I think the flywheel only has to be replaced if there is a significant degree of slippage before you bring the car in, as was my case. So, if you catch a slipping clutch quickly, you may cut down on the cost of the repair significantly.

My car's clutch was replaced at a Toyota dealership in Minnesota.