8-speed 105 shifter shot - replace or upgrade?
I recently bought a late 90s Team Saeco replica Cannondale on craigslist (for $400). Frame is CAAD3, in like-new condition, carbon fork, full 105 gruppo. I was having a little trouble with the rear shifter during a test ride, but I wrote it off to the derailleur needing adjusting (clearly, I'm not a mechanic). The chain and rear cog looked a little worn as well, so I figured I was in for replacing that as well, but again...no big deal.
Bring it into the shop, and the mechanic busted out the chain tool and pointed out that I'd need a new chain and cog, otherwise it wouldn't ever really shift right (as expected). He pointed out that 8-speed stuff is hard to come by, but was pretty confident he could put an 8-speed mountain cog on there, as the rear cage is pretty long. Ok, so far so good.
After some testing, the mechanic gives me a call to tell me the right (rear) shifter is shot. Says he can order a new one, but its about 150 bones (in addition to other work to be done...chain, cog, derailleur adjustment, etc), and again reminds me that 8-speed stuff isn't easy to get.
At this point it seems to me that if I'm going to be buying a new shifter, I should be just putting on a new 9-speed, especially as I'm replacing the rear cassette and chain anyway. The guy starts listing all this other new stuff I'd have to get (wheel??) and points out it's substantially more to do that.
I don't think the mechanic is trying to give me the runaround at all, isn't trying to push me into doing the repair, etc.
1) What is really required for me to change from the existing 8-speed rear to 9-speed? How much will that set me back?
2) If I stick with 8-speed, what shifter should I be getting, and where?
3) If I'm going to spend $200 on this repair, does it really make sense to stick with this bike? Or should I try to resell it for what I paid and look for something with less headaches (not easy to find in this size/performance/weight class)?
Help is greatly appreciated - apologies for being a dum bass.