Small Engines (Lawn Mowers, etc.): J D 180 transaxle, pinion gear, transaxle

Question
I am looking at a 180 mower and the owner says when cutting grass it will sometimes jump out of gear.  Is this a common problem and what could I expect to spend to fix it?  Sorry to not be more specific but any ballpark comments would help.  Thanks

Answer
Replacement could run from $100-500 depending on just which transaxle it is.  It could be the pinion gear jumping around.  That happens sometimes.  You'd really need to open it up to see what's wrong.  Usually these are just replaced and not fixed, but every once in awhile you find one that's worth fixing.  Thanks, PK.