Get a good used steel bike and install whatever groupset you can put together within your budget. Trek, Centurion, Specialized, Miyata, Fuji, Raleigh, Univega (they made one or two decent steel road frames, besides their usual mountain bikes and hybrids), many others made good mid-priced chromoly steel road bikes throughout the 1980s, all very comparable frame quality, groupsets, wheels, etc.
There were also lots of high tensile steel frame bikes from the 1970s-'90s but they'll be heavier and often with other compromises: cheaper groups, maybe steel rims from the 1970s. A giveaway is often the "turkey" lever "safety" brake. Not really as bad as some purists claim (some could be adjusted to get decent leverage for slowing, although I wouldn't rely on them for serious stopping power), but a good indicator of a lower priced bike that often used all or mostly high tensile steel frame and/or fork. The steel rims were worse than the turkey levers -- steel rims don't brake well when wet.
With the pandemic effect on the bike market, good used bikes may be in short supply in some areas and overvalued, but be patient, shop around and pounce quickly when you see a frame with potential.
Availability and price seems to vary depending on region. For a few years the Centurion Ironman was often available for $200 or less in my area (pre-pandemic). I snagged one in 2017 and could have bought another two or three for the same money or less over the next couple of years. The guy I bought from said a batch of 'em were discovered in a warehouse, unsold but in varying condition depending on storage conditions. Mine appeared to be unsold, in good but not great cosmetic condition -- a few paint scuffs, nothing important.
The 1980s groupsets, mostly Shimano and Suntour, were very good if you don't mind downtube shifters. But it's relatively easy to switch to integrated brake/shifter setups from MicroShift, MicroNew and others without changing anything else other than cables.
Most of those came with 6 or 7 speed wheels with freewheels, which limits us to 7 speed cogs at most. I still have one old freewheel wheel but my others are freehubs for cassettes. I can swap wheels without any indexing problems. The bike doesn't care whether it's 7-speed freewheel or cassette, as long as the cog spacing and tooth design are compatible and the cassette spacing is aligned the same as the freewheel.
The most I've upgraded to on my older steel bike is an 8-speed rear derailleur and cassette, with appropriate shifters. Some folks on the C&V forum here have posted pix of some complete overhauls, retaining only the frame but replacing everything else: carbon fiber fork, 10-speed drivetrain, even carbon fiber aero rims. A local friend loves old school high end steel frames -- Merckx, Colnago, others -- but not the downtube shifters and limited 5, 6 and 7 speed groups, so he installs new drivetrains. Sometimes aero rims but not always.
I have a couple of carbon fiber bikes too -- a 1993 Trek 5900 (their flagship model umpteen millennia ago) and 2011 Diamondback Podium. Honestly, the steel bike rides better on our increasingly bad chipseal roads. And I'm not consistently strong enough to notice any differences in average speed over my usual 20-40 mile rides. Maybe a second or two faster on climbs but we don't have many long climbs, mostly rollers with lots of short, steep hillettes of 5-12%. Of the two the old Trek rides nicest, although some folks criticized the older Trek OCLV frames as feeling dead. It's not a crit type frame, but I don't race so I don't care.