I've bought a 2nd hand Bearcat UBC 200XLT for 40 euros. Works fine. (Unless you consider the worn-out battery, so I need it on external power at all times.)
I built a basic dipole antenna to use at home (it's hanging in the attic) instead of the whip antenna that comes as standard. That sounds complicated but it really isn't. It took me about 10 minutes to fabricate it using stuff I had lying around the garage anyway. It greatly improves reception.
However... I still consider it money not well spent. I should have saved it and use it towards buying a transceiver instead. (Icomm seems to be the standard here.) You can use a transceiver to listen in, but you can also use it as a backup in the plane while flying.