I had a friend who bought a 737 second-hand in non-working condition for $700, thinking he could put new tubes in and flip for a profit. After I replaced the tubes, light bulbs, molex connector, regulator, and caps, he paid me around $300 for parts and another $350 for labor. Around LA, you're lucky to sell a used 737 for $1500 because most people know used units may soon need work. Maybe he made a couple hundred on the flip.
He would have a nice unit for the money if he wanted to keep it for himself, but if anything else was wrong (pots, meter, switches, etc...) it would have been a loss for sure.
In this case, it's a great but costly learning experience and you'll hopefully wind up with a unit that you use and love. I love 737s on bass (Inst input) and for voiceover work, plus they do look great in the rack to clients.
I hope yours turns out great in the end...