Optical sensor for use with retroflective tape

[Tom Line]

I know many teams used retroreflective tape and an optical sensor to measure wheel rpm last year. I'm curious if the ones who did found a good low-cost sensor. We're in a space crunch (as I suspect everyone is!) and don't have any way to attach encoders to the drive shaft.

I've found a few optical sensors that are retroreflective. Some are either ridiculous-expensive. For instance, $100 for a banner sensor. Others are nice and cheap in the $12 range, but don't list a maximum switching frequency! We're looking at rpm's that may range up to 10,000.