Right...well a modern F1 engine can be lifted by one person. The V8s probably only weight about 70kg now if that. With regards engine life....if you turn them down to 15-16,000 rpm they'll last a very, very long time. There is a Gould hilclimbe car running an Arrows-HART V10 from 2002 that revs to 15k and they reckon they can get an entire season out of it between rebuilds. I'd hazzard a guess at maybe a rebuild every 6months depending on the use and if someone has the money to buy a V8 Cossy engine then I'm sure they can afford the rebuild.
As for the reality of it....hard to say. It's not beyond possibility as Cosworth very sadly no longer have a car to supply next year so it's possible they'd sell an engine from this year to a private buyer as they're going to want to get some money back.