By the way, a local antique shop has a TRS-80 Model III(what the one in the listing appears to be, unless it's a IV) for $250 or so. It also hasn't moved in at least 6 months, so I'm not sure if that's necessarily an accurate marker of current market price.
I haven't kept up with current Ebay prices, but it wouldn't surprise me if $100 isn't
too out of line considering what it would cost to ship one of the beasts.
Of course, most of them haven't been sitting in a back yard covered in a tarp

. I wouldn't put a lot of faith in the one in the ad working unless some serious work were done on it.
I've wanted a TRS-80 since I first played with one that a friend's dad had used and retired. His started life as an all-original Model I with 4kb of RAM and no numeric keypad, but had been upgraded to 16kb and the numeric keypad. He had the original monitor, cassette player, plus the expansion unit with an additional 32kb RAM as well as two floppy disk drives, a printer, and a modem to attach to it. All in all, it was a pretty slick set up for a TRS-80 model I, although we needed his dad's index card with the power up instructions to get everything working correctly and talking to everything else.