Hi Stiggers and
Mk2 180's seem to go from ?1000, up to ?4,500, depends on condition and how quick they want to sell them.
I've got a derv but picked up from on here that its best to have the belts done, age and miles means they are all due by now. Prices for getting the belts done range from ?500 to ?900, so best search on here to see the best people to do them.
Power and vis motors need checking easy fix but make the cars run awful if not right. Plastic manifold needs checking, as well as the clutch, as its plastic it tends to go.
Stamford has done a guide on the 180, which will be a great help for you.
http://www.themgzs.co.uk/vb/showthread.php?t=11254
http://www.themgzs.co.uk/vb/showthread.php?t=11255
Hope you sort out a good one.