Hit me up if you find some bikes you like and I can give you the 411 on whether or not they're a decent value or not. Like I said, cycling is a lot like golf, photography, and musical instruments in that you can go cheap just to "do it" but once you get into you realize very quickly how bad the low end stuff is in terms of value. You can probably find something used for well under $500 that would be perfect for a beater city cruiser but you'll definitely want to find a bike shop to help you keep it in running condition. Unfortunately looking through the used bikes on CL for Nashville shows mostly the crappy low end mountain bike garbage but there are some definite deals out there.
Check these out:
https://nashville.craigslist.org/bik/d/1983-schwinn-world-sport/6579738466.html https://nashville.craigslist.org/bik/d/pink-bianchi-road-bike/6581615009.html Bianchi makes some great bikes (I have a Volpe that's great) but their geometry is a little weird to me. Before you start looking for a bike stop by a well reviewed bike shop and have them do a "quick fit" for you and some test rides on different frames to get a feel for what you like. If you have the tools (level, measuring stick) you can use this calculator to get an idea of what your bike frame size is but a shop usually can size you up quicker.
https://www.competitivecyclist.com/Store/catalog/fitCalculatorBike.jspI didn't get sized when I bought my "first" road bike back in 2012 and I wound up riding a frame too small for a while that caused some serious issues with my IT band. If you decide to buy a new bike from a local shop they'll usually throw in a "fitting" to make sure your bike is set up right so it's comfortable and there are no mechanical problems. Much like with golf club a fitting makes a huge difference in performance and comfort. I have kind of a strange body (6'3" but very short legs) so I have a hard time find frames that work for me without major adjustments.
My main bike now is a Surly Ogre and I actually switched it from the XL frame to a L after a couple of months because I couldn't get the fit "right". It's a weird looking bike but for bike packing and touring it's a really hard frameset to beat, especially for the price. By no means is it fast or nimble but it's probably the best "swiss army knife" bike out there now.
https://surlybikes.com/bikes/ogreOne bike you might like is the Surly Pack Rat (
https://surlybikes.com/bikes/pack_rat). It runs 650b or 26" wheels (smaller wheels, very nimble), has a rack, and comes in a really sweet green. One of the really nice things about Surly bikes (other than being steel and very affordable) is that you can easily remove the decals. Great if you want a really clean look. Also great if you like to change things up.
