An office near me (we're moving into the same building) recently cleared out a lot of old hardware. I found 2 rMBPs among the 'broken' pile. One didn't boot, the other did boot but had a smashed screen. I took both, swapped the screens, and now have one perfectly working 2014 mid-range rMBP (2.5GHz, 16GB, 256GB, GT750) /for free/. Could not believe my luck! Easily fast enough to keep up with the current machines.
I had it listed on Facebook for two weeks at $1200 with no offers. I live in a fairly poor area though, so I ended up driving to the nearest city to deliver it too.
One man's trash ^_^