Trying to find an inexpensive vintage or classic for my son; not really collectable, magical, or high end. He's only 12 and a little short so I have to get something around 52/53CM. I got lucky last week and found a 1989 Trek 1200 Aluminum at a good price but its just a tad too high for him so I am hoping to keep it for myself. Anyway - that gave me the bug to go look for something else.

We hit 25 garage sales today. Only one had even a flat bar mountain bike. Nothing else. Yes, Twenty Five.

Went to 4 thrift stores this week (TEAM, 2 Goodwills, and Salvation Army.) Was shocked that Salvation Army wants $50 for a ragged looking Next type mountain bike when I think thats about what they cost new. the TEAM store had the rattiest upright bar cruiser thing, with wheel hard rusted. Goodwill had nothing

Went to three pawn shops in the area. One had some crappy cheap mountain bike for $58, one had no bikes, and the other only had the same old walmart mountain bikes.

I've been scouring Craigslist too all week and haven't really seen anything that looked promising.

I've read here where you really have to look, but I get jealous when I see all the finds. I know I'm a noob at this - but is it normal to come up with a zero like this? I figured I would see maybe 3-5 bikes, and they would either be too expensive, wrong size, or even too worn out but this was depressing.

FWIW I live in Houston and we hit the Tomball-Magnolia-Spring area. I am willing to drive as far as Waco and Austin but Austin has hipster fixie fever. I figured maybe since Houston has never been a big cycling mecca it isnt the best place to find deals - but when I look at the prices in Austin I also get discouraged.
I was thinking maybe some of the smaller towns would be good, or even hitting the big flea market tomorrow. I figure the police auctions might be good, but could also be filled with flippers or noobs like me.

Pricewise I'm looking for $100 or less, and really wanting indexed (but realize brifters are out at this price)

Any tips on where to lcoate something rideable? I know cables, tires, and tubes will be needed. I have decent wrenching skills and have built up two bikes since getting into the hobby in March, although those were mainly just bolting up already good parts and adjusting as opposed to restoring.