Where to buy old version of Production Premium

Hey all,

I was wondering if anyone out there had some advice for where I could buy myself a copy of Production Premium, either 5 or 5.5 (chances are I wouldn't be able to afford 6). There are a few websites out there that claim to offer it but I'm a bit hesitant to fork over hundreds of dollars to purchase off of sites I've never heard of before. Does anyone have some tips for finding legitimate copies of old adobe software?