Agree with Chimbu,
Most older aircraft have some corrosion especially if they have been parked for a while.
The main issue is the airframe in good condition.
Was it hangered , parked outside or parked under a shelter.
Market price is about $60,000 for a good example of the Rallye 180 , the German seller is asking $26,500 . If you can get it for $15,000 and there's not too much corrosion in the airfame it would be worth looking at.
Here's a Rallye 235 in Spain with half the total time, engine 200 hours since overhaul and looks in good shape for $60,000. You could probably get this one for $50,000 and enjoy it straight away.
