Even if this needed an entirely new engine/trans (which is likely because it may have low compression, which could explain the oil leaks everywhere), if the body and everything else was in good shape (which it looks like), $5000 is a steal...500s in decent nick are like $12K-14K in Canada, if not slightly more.
Buy a cheap FIAT 126p engine/trans in Poland and ship it over...swap it in and you’d have working 500 for a very reasonable price. 126p engines are pretty much plug and play with a few minor, easy parts swaps (starter, some engine cooling tinware, rear engine mount) and the entire engine/trans and rear valance can be unbolted and just slid out backward as one complete unit. Plus 126p engine means SYNCHRO gearbox with slightly more power (23hp or so vs 18hp in the 500's original engine) and the 500 originally only had a non-synchro gearbox.
I SOOO wish I was closer to Ontario and had a place to buy, store and work on this right now.....you have NO idea!!!
Any Ontario Oppos want an awesome project for a reasonable price that would be ridiculously easy to work on???