I think a Lemond from the late 90's/early 2000's would suit you well. Steel frame, horizontal top tube so classic styling and construction but with more modern stuff like integrated shifters, threadless fork, vertical rear dropouts, etc. They're also not particularly collectible so that keeps the values down. Just checked my local craigslist (San Francisco Bay Area) and I didn't see any for over a grand, most in the $400-$700 range.

I'm personally a long time Cannondale nerd so of course I'll recommend them. They're all aluminum back in the day and kept the horizontal top tube for a long time. Quality bikes, fairly abundant so fairly inexpensive. I will say though to be aware of frames made during the mid-90's as all but the touring models had a goofy rear dropout that was looooong and sometimes problematic. Last year I of that I think was '97. Anyways, they're easy to spot, the rear dropout sticks like an an inch a half out past where the chainstay and seatstays meet. What was problematic about them was the dropouts pointed forward and made it possible to pull the wheel out of the dropout when hard on the pedals. I've seen it happen on more than one. That damages the droupout and makes it more likely to happen again. They fixed the issue by simply going back to a conventional vertical dropout in the late 90's, so start your hunt there, if you choose.