Question for you Apple crazies

My home is paid for, and I'm moving to a place where housing is about
half what it is here, so if I buy something about the same size, I
might have enough left over to buy an Apple product... So some
questions:

Most important, is there any point in shopping around for the best
price on a Macbook Pro, or is the pricing pretty much fixed?

I see that there a lot of listings with years mentioned. How far back
can I go to be able to dual boot into Windows? How far back to get a
great retina display? And how far back to get great performance,
something that is more than adequate for LR & PS, video and audio
editing? How far back where I can still easily add a second high
quality display?