Before I bought a code reader, I'd get a used full function scanner. Code readers can't do things like cycle the grid heaters, read transmission data or do power balance tests on a 24V... and the list goes on. There are TONS of old scanners on Ebay. Snap-on recently discontinued Software Support for the MT2500 Scanner. It's a great tool, but it's been around for 18 years. Be careful what you buy though. The only functional diference in Snap-on Scanners from 1988-2007 is the software cartridges. For whatever reason, most guys are selling them without the software.
Look for one with Primary Cartridge Coverage at least as high as the year vehicle you own. If you keep your eyes peeled you can get one in the $300. 00-$500. 00 Range.
joe