My 'old man' rides a 1983 steel frame Terranaut that he considered replacing last year. Instead of spending $4k on a new bike, he stuck with what he liked and knew fit him perfectly.

He upgraded every component on the bike to Ultegra. Downtube shifters to brifters, cassette, crank, brakes, hubs, wheels, pedals... everything. He says it's like a brand new bike, and regrets not doing it earlier.

He spent $1300 total, including install. Check out PBK for component group in your price range.