Also, don't limit yourself to Masterpieces. I got back into Transformers for Nostalgia's sake too, but having owned only MP-01 and MP-11, I'm over the Masterpiece line. Both were fiddly, poorly balanced, and MP-11 barely held together properly in either mode. MP-10v is so far excellent, but it's a complete KO in all aspects.
My strategy thus far has been to carefully pick KOs in any scale, and legit releases in Deluxe and Legend scale. I've been able to very quickly wind up with more Transformers than any other toy line I collect this way, and so far I've been pretty happy.