data logger

I'm very interested in a data logger. tmo.com wants 300 for the wire and software. Digitaltuning.com (pocketlogger) wants 175 and plugs into a pda. (Maybe they both utilize a pda) Is pocketlogger a recomended brand name? What type of pda should I buy (series, model #). Am I headed in the right direction? If not feel free to recommend a new approach. Replies are always appreciated.