Look for cracks around the lugs. Cosmetic stuff can be repaired, but the lug/tube connection is important, and cracks are bad news.
Tires and pedals are what bke resellers take OFF if they're good, put ON if they're disposable.
roccobike is dead on about 600/Ultegra STI shifters. I have idetical sets of 8-sp STI's, one in 600, one in DA. The 600 is simply a quicker, lighter shifting version of the DA, for some reason, maybe lube, but it's like that.
I'd look the bike over and confirm the frame condition as pass/fail.
Then, I'd look it over again, ignore the frame and look at components. Make a list of needed vs. OK.
If the frame was fine, cosmetically repairable, and the components were fine, I'd go $275 and negotiate up using tires and pedals. Pedals are very often not sold, personal items, so you won't get much traction there. Tires, you can use as a bargaining point.
I'm like rocco..when I see a bike for sale, I look at it with modern STI in mind, and what kind of bike will it be after the upgrade, condition and investment-wise? Then I either pass or pull the trigger. I don't buy bikes, hoping to make them better at a reasonable cost. I either can or can't.
You shouldn't change the Frisbee.
1985 Raleigh Racing USA - Coleman's Competition
1984/85 Klein Performance
1988 Centurion Dave Scott Ironman Master
1989 Centurion Dave Scott Ironman Expert
1989 Centurion Carbon R