The very cheapest cyclocomputer (unless you buy something from a place like DX) is this at $13. It even has a number of features that many computers don't have -- thermometer, backlight and calculating moving average (rather than simple average) in particular.

However, it does have one flaw -- the screen goes black in full Texas summer heat when in the sun on an unmoving bike. Like this, but that's after it's cooled off some. It can easily go completely black. It doesn't hurt the screen, but you can't read it while it's in that state. It might be OK in Idaho, but here there's a few months a year I'm tempted to replace it.

It's also a bit bigger than some other models, and the sensor has to be really close to the magnet to work. But it's hard to beat it for the money, and saying "Schwinn" I'd say it's less likely that somebody will steal the head unit off your bike