Someone on AW actually did try the whole resister thing a while back. From what I read, it looked like way more of a hassle then just replacing the damn things. Yeah, they're expensive, but do you really want to make a rats nest of wiring inside you engine compartment? Not to mention spend hours and hours to get the damn things to send the right signal back to the ECU? Don't do it man, just replace them.

You can get away with used ones, but it probably won't be long before they fail as well. Last I checked, they go for around $100 used in the classifieds. Back when mine were bad, I just coughed up the dough for brand new ones cause I didn't want to spend 200 on used and have them fail a month later. Knowing my luck, that's exactly what would've happened... In the end you'll be happy that you did it the right way, and chances you won't ever need to replace them again.