Using flash drive as swap

I'm in the process of building a new home server, in a converted big hulking heavy steel AT server case, that will mostly get used for file serving, local http serving, and routing / firewall between my wired home LAN and the wireless router to/from the Internet. One of the setups I'm contemplating is using a $50ish flash drive as a swap partition and/or disk cache, and I'm wondering if this is a good idea. I know that it might not be as fast, but it might allow the HDDs to spend more time spun down.