I was in your position a while ago, and got a regular old cateye. However, I have recently upgraded to a Garmin Edge 205, which I bought used from someone on this forum for only $100.

There are some big advantages:

1. Only one thing to put on your bike. Nothing on the spokes, no wires, no sensor.
2. It's rechargeable, so you don't have to buy new batteries.
3. You can customize the display, and choose a lot of nice information (including sunset time)
4. You can share and keep track of your rides automatically.

http://connect.garmin.com/activity/80641139



So, if you think those advantages might be worth it, look for a used GPS.