I have the Virgin Mobile LG Optima V, which is $150 now and goes on sale for less periodically. That's $150 unsubsidized and with a month-to-month, no contract plan. It's not the greatest phone in the world but I'm largely satisfied with cost/performance tradeoff.
Covered here previously: http://news.ycombinator.com/item?id=2171107 My write up on how to activate the Optimus for WiFi use only: http://blog.gerundinganimal.com/2011/01/cheap-wifi-only-andr...