There are only so many pre-3.56 consoles left out there...and far fewer with PS2 support...you can get them used all day, but then you are probably getting a YLOD-repaired unit or one on the verge of YLOD anyway. Do you have any idea how much a NEW BC console costs???
A proper repair doesn't have to be temporary...YLODs usually only come back when you fail to address the cause of the YLOD, and a reballing can make the system more reliable than it was from the factory...again, if you address the reason why it failed. My 40GB had a YLOD so long ago that I didn't even know it was a YLOD because no one knew that you could have a YLOD without a yellow light...a few minutes in an oven and a fan speed fix and it is still going, it has lasted longer since the YLOD repair than it did before it got the YLOD. Granted, I have done some crazy stuff to it since, but that is only because I wanted to...none of that was actually needed. Not only did this system last longer after the YLOD than before, but I got a PS3 slim a good long time after the YLOD, and the slim started having problems while the YLOD-repair system kept going.
So, is an afternoon worth the $800 price of an unopened BC unit? I think most people would say yes...in fact, I think most people would think that it is worth an afternoon to fix a 40GB system on 3.72 firmware even if they didn't intend to downgrade (can't downgrade the new ones).
Anyway...even if it wasn't worth the time, I would still want to repair it myself...I love playing with electronics, I love fixing things, and I hate waste. If you want to throw away your YLOD'd system, GREAT...I'll pay you $50 to ship it to me.