Craigslist and ebay and shop for used ones. I just yesterday sold some rollers for $40 that just needed a belt. I got my Minoura rollers with a Mag unit and handlebar support (to emulate a trainer) for $50 on Craigslist.
And here's a set of Kreitlers for $275 up my me: http://milwaukee.craigslist.org/spo/3444284934.html

Most rollers and trainers, based on my observations, get little to no use so almost any you buy used should usually be in okay condition.