Also, i've decided to take the thing to a vintage repair shop to do the following: get the frame powder coated, the engine cleaned up, polished, and maybe powder coated too, getting the tank repainted, the carbs rejetted, and a new seat upholstered. they're asking for 2500$. Is that a reasonable price?
If you are willing to pay the money to have someone else do the work, then $2,500 is very reasonable. Powder coating a frame is about $300. Repainting a tank is likely to be about $600-$1,000 of that money (depending upon the quality of the work).
You can’t powder coat the motor unless it is completely disassembled to the bare cases (figure $300-$400 to do the disassembly). Powder coating the motor is another $400. Then reassembling the motor is going to be another $300 in labor, plus any and all baskets, seals, and rebuild kits.
None of this accounts for any custom changes or “upgrades”.
The 650 was a bit of a red headed step child in the SOHC (single overhead cam) world. It was more of a cruiser than street sport. The frame is different, the seat is dropped, the bars were more upright. All this makes for more difficult and more involved customization to a “cafe/brat”.
Here’s a bit of advice you haven’t gotten: consider abandoning THIS bike and find a CB 550 model between 1973-1978. There should be plenty out there. Easier to work on, easier to customize, better looking. Heck, I’ve got a 1.5 customized frames sitting in my “get rid of” pile.
There’s frequently folks on here trying to unload parts bikes that would be a better starting point for a first bike, first project.