schwinn wireless spedometer from walmart for 15 dollars. Buy an earth magnet and glue it to the rim and align it with the wireless reader...pretty accurate and updates every 1/2 second or so.
For tachometer check
ebay, someone may have a link, but theres one for 15 or 20 bucks that reads up to 16,999 RPM, correct me if im wrong please! Not sure if tachometer is reliable but from what i hear its good. but the speedometer listed above is a definite cheap good investment, just have to get your hands dirty a little bit with the glue and earth magnet.