"Prey" is one of those out-of-print graphic novels that always seem to sell for a high price on Ebay (something around $30 for a used book whose cover price was much lower, if I remember correctly)- but there are plenty of trades floating around comic conventions and the used shelves of comic stores, for only a few dollars, if you have the patience to look.
I kept an eye on on Ebay for years, but rarely saw one go for cheap. Finally, I bit the bullet and picked one up for more than I should have on Ebay. Not three weeks later, I found one in a comic book shop for four bucks. And then two months later, I saw SEVERAL copies for sale, also for only a few bucks, at a comic convention.
ARGH.
Anyway, it's a great story and a great followup to "Year One" - way back when "Legends of the Dark Knight" was really focused on Year One-style stories.