to fix it right, you likely will have more in it than a new one. That's just the way it goes. That said, you're better off to buy a good running one that's in nice shape
Here's an example of a project I have, it's a mod project and I really don't care what I have in it.
Project saw $300
new berrings, gasket/seal kit, $100 buy the parts from Stihl, correct berrings and better quality seals
crank is bad, so a good one from my parts stock valued at $50
Cylinder, again from my parts stock but it takes $50 or more to get a good one
Piston, OEM $125 or Meteor $45 Wrist pin berring and new OEM pin, clips, $40
Fuel line, impulse line, intake manifold, filter, carb kit $80, $$ add up fast.
new elastostart cord $20
Now add up fixing stripped holes, running around, msc supplies and all the little parts that I forgot, buy a dual port cover, or a different handle bar, clutch cover, dawgs, and you can spend a bunch more. I had a nice wrap handle bar, flared clutch cover and big dawgs on hand or from other saws allong the way but I still had to buy them or they have value to sell.
It takes the right tools to split a case, or pull a flywheel, don't just go splitting the case beating it apart on the crank.
I know projects are fun, and we all have our own reasons. I wanted a 660 so I bought a brand new one for $900 west coast version. It was likely less than what I'll have in this one I'm working on. I've accumulated a couple other 066-660 saws from good running ones to project ones and a pile of parts, but the new one wasn't a bad deal.
I've got a few of these saws, and I should thin them out a bit and let one go. I'll kick it around a little and may advertise it. It's a good running late 066 mag, been well used, I bought it used with intentions of such a "refurb" project but it runs to well to mess with and we use it quite a bit. But I've got lots more saws and a new Dolmar 7900 that's a joy to run.