How many speeds in the rear? IIRC, if it's fewer than nine, there will not be compatible brifters ... and changing that out will require a new rear wheel and cold-setting the frame to accommodate the wider hub.

I'm still thinking about updating my 1987 race bike, which has a 6-speed freehub. But it's a BIG job, and yes, expensive - brifters, rear derailleur, rear wheel with cassette, and the frame work.

My old bike is a good enough frame to deserve it. It sounds like yours might be, too. But it's not for the faint of heart or wallet. At least this is a good time of year to be contemplating something like that (if you're in the northern hemisphere).