Rear engine seal leak?

I ve had a big oil leak since i bought my car a couple months ago and the guys at the oil change place said its my rear engine seal...is it expensive to fix? what are my alternatives?
I have a 1998 cavalier z24 2.4L

To replace it, you have to remove the transaxle from the engine... probably 8 hours or so for a M/T, and probably a couple more for an A/T. The alternative to fixing it is not fixing it. You could try a bottle of engine oil "stop-leak"... all the stuff does is make seals swell up, it may at least slow the leak until you can afford to replace the seal. Just be warned that it may make other seals leak a little bit. Also change the oil every 3 months or 3k miles, clean fluids don't start leaks and it should at least keep the leak from getting worse.