There’s a long running thread in the classic and vintage forum about converting old rigid mountain bikes to drop bars. There are special problems related to the cable pull needed by the shifters and brakes.

You’re best off starting with a 7 or 8 speed Shimano bike from up to the mid 1990s that has cantilever brakes, not V or disc brakes, because cantis take the right amount of cable pull from drop bar brake levers. And then using bar end shifters, because an eight speed shifter on the right will also work on a seven speed giving you more options and the left side will be friction so the different mountain versus road front shifter cable pull is not a problem. You probably should not choose a SunTour bike because Shimano went on to become standard in the industry for this stuff while Suntour gave up on shifters and switched over to suspension forks.

The idea of going down a size to reduce the reach is on point, but the extra reach comes with not enough stack. So you also may want a taller stem. That’s all right, you needed a new stem anyway to go with a different clamp diameter of the drop bars.

Show Your Vintage MTB Drop Bar Conversions

if you are having trouble searching craigslist by inch sizes, try also looking for letter sizes. You are a medium and you are looking for a small. But to be fair in the price range you’re looking you are just as likely to find them listed as anything including “old bike just needs air”