Or an alternative, find an used Tektronix probe isolator, basically this gadget turns your ordinary scope's probes into a fully isolated and floated ones.
At the market, these used isolators are "relatively" much-much cheaper than a full blown used isolated scope you're looking for, but alas, it has the same problem as we discussed before, as it came with its own special prorietary isolated probes standard accessory, so if the seller doesn't include it, again, then probe isolator will become an expensive paper weight.
As an hobbyist, I had been thru the path like yours actually, in the search of scoping mains related signal, and at some gadget, I had to wait for years to get a decent priced one, so I think I can feel your pain.