Cheap computer that allows downloading of file
 

Is there any cheap-ish device that allows me to download and then graph speed over time? i want it for lap times on the track.

so far I've found the Mavic WIN-Tech USB Cyclocomputer ? any others that are good?

See the Garmin Forerunners. The 205 is fairly cheap, a lot less than the Garmin Edge bicycle versions.

But, the GPS might not be as accurate on a short track, since it may cut corners in between the location samples.

correct I do not want something GPS based. Wheel sensor based will be most precise for this purpose.

Get a Garmin and buy the separate speed/cadence sensor. also, I hav found the gps to be very accurate. Use amazon and get a Forerunner 305 for 140. The speed sensor can be had for about 35 bucks also. Bike mounts are 1.75 a piece from amazon Bostic outfitters store.