I just recently purchased an OBDII Reader. If you want to just read the codes and reset the Check Engine light, that's all you really need. A reader will point you in the right direction for the cause of the fault and will be cheaper, around $100 or so depending on brand and where you buy it.

If you need more detailed info with sensor readouts, graphs, charts, etc. you will need an OBDII Scanner; typically software that will run on a laptop or PalmPilot. They do provide more detailed info, but it's cost will be significantly more.

If you do a search in this forum, you'll see more info from people who also contemplated getting one of these toys.