The LM1 from Innovative is the industry standard for the home/ hobbyist/ amature 'tuner'.
You can add all sorts of data acquisition with it, but they aren't necessary.
I have read plugs before, with leaded fuels it's easy enough, but by the time the new unleaded (especially this new 'reformulated' gasoline that's out there) by the time it's colored the porcelin, if it was going to do damage, it already has.
Of course if it were off far enough to hurt itself, you would expect other symptoms as well.
Check Fleabay and Craigslist, there isn't much that can go wrong with them, except for the leads (ie right at the O2 probe).
