I will be happy to keep my eyes open however the next one I find (if I am THAT lucky) is going to be mine and be transformed into a .22 Mag. Just check the classifieds often, I was lucky enough to find one here and jumped right on it before others here did, they are few and far between, the one for $139 sounds like the way to go and if you want you could sell the second .410 barrel to help offset the price....
You should not need a lathe to do the rechamber, just a handle to turn the reamer and plenty of cutting oil, go slow and easy with very little pressure and check often. Ask the rental company for hints on it's use and which style you should get for your intended use....<><....