I have a 2001, it's been a great car, reliable and trouble free. My non-techical wife has done most of the driving and she loves it (I drive the 2004). However, if I were getting a new car I would get a 2004 for later. There are over fifty chapters of improvements in the Prius 2004 New Car Features manual from the 2003.
1. There were only 53,000 imported into North America so used parts can be a hassle.
2. You don't know how it was maintained, although it's hard to disguise poor maintenance on a ten year old car (if you can get the previous owner's maintenance logs this won't be a concern).
You need to get it (or any used car) checked out by a mechanic familiar with that particular car. Also you need to check for title and accidents.
www.ctvbc.ctv.ca