At http://www.circuitcity.com/ssm/Prepaid-Wireless-Phones/sem/rpsm/catOid/-12830/N/20013161+20016441+20012830/rpem/ccd/categorylist.do you can get a few of Virgin Mobile's phones for cheaper than anywhere else.
The Slice is $29.99 there with free shipping (though I'm sure tax applies), beating Virgin Mobile's own site by $10 plus tax (whew, who ever thought a phone thinner than half an inch would be sold for $30 prepaid?). If there's a store nearby you can pick one up there.
The Audiovox 8610 "Vox" (yeah, the old phone) is $17. You have to pay extra for shipping though, and tax...so not a great deal (old phone anyway).
Oh, and the Kyocera Oystr is $10 (plus shipping, tax, tax on shipping) but it's not a great phone anyway.
Last but not least, the Switch_Back, as seems to be the trend, is down to $80. Nice if you need a phone with a keyboard.