If everything you say is true, it certainly sounds very undervalued. However, the only way we can provide a proper asessment if if you post a good, overall, drive side pic and some pics of the tubing decal and major components. Knowing the model number/name and serial number would also help. The serial number should be on the left side of the seat tube, in the vicinity of the front derailleur clamp. Finally, we need to know where you live, as value is highly dependent on local market condidtions.
It's the side that the derailleurs are mounted on. When pictures are taken from the opposite side, as you have, it's very difficult, if not impossible, to identify the crankset and derailleurs. Being able to identify these components provides a valuable aid in identifying the level of the bicycle.
The stem shifters and safety levers indicate an entry level model though the cotterless crankset, what appear to be aluminum rims and front quick release skewer, indicate it is not bottom of the line. I'd still like know what the tubing decal says and the brand and models of the crankest and derailleurs.
The condition appears to be very good, though I wouldn't call it excellent. It has two flat tires and the tube has shifted in the rear tire.
I imagine Missouri is a pretty depressed market, especially at this time of year. However, at $12 it is severely underpriced. If you wait a couple months and rectify the tire situation, I would think that this would bring in the region of $100, maybe more, depending on what the tubeset, derailleurs and crankset are.
Clean it up, get air in the tires, take much better pictures, use a photo hosting service, sell through C/L, and you should be able to get about $50. But if you don't want to go through the hassle, just donate to the charity of your choice.
What I can see of the bike (stem shifters,stamped dropouts, turkey levers, nutted rear axle, (the following are guesses:claw derailleur hanger, high ten steel frame, etc.))= close to entry level. Alloy rims are a nice plus. I could not get $100 for that bike, without installing new tires, cables, housings, bearings and grease. Not worth that additional expense, unless you plan to ride it yourself.