I'm looking to invest in a bike computer for ~$100. Any suggestions?

what features do you want to get on it?

whatever i can get for the price =) definitely speed and altitude

I would get wired CATEye Astrale8 and invest extra in to extra bibs and a jersey.

If you want altitude, get a VDO MC1.0 (I recommend the wired one over the wireless one).

If you are at all competitive and like to track your times, stats, data, etc., I recommend a Garmin Edge device if you can find a bit more money in your budget. It is an awesome device and it allows you to use Strava, which is amazing. www.strava.com