I just posted an item on Prepaid Phone News about using a closeout Palm Pixi Plus on the US prepaid MVNO PagePlus. These phones are going for $65 or less brand new on Amazon and elsewhere. They are Verizon CDMA models and as far as I know won't work on any operator except Verizon or an MVNO that uses the Verizon network like PagePlus.
However, the Pixi Plus has WiFi and it's possible to use one for app development or as an MP3 player and WiFI only mini-tablet by following a bypassing activation using some developer utilities. Details are on the HP Developer site