It's one of the best zooms made by Pentax (not counting the *-series), and pretty sought after. I've got two, just in case I loose one. It shouldn't go for less than 125 USD.
$125 USD? Wow. I wonder if it's really worth that much. The member above posted a link for the same lens selling for $72 USD. Although, that eBay description reads like it's a bit inflated. This is not a DSLR lens. Although it might be compatible, that ad doesn't ring completely true.
Of course I might know zero about Pentax lenses...