Mwave offers the PowerLink 150Mbps 802.11n Wireless USB 2.0 Adapter, model no. PL-14N, for $19.99 with free shipping. That's tied with our January mention and the lowest total price we could find by $6. It features a max speed of 150Mbps, dual 7dBi dipole antennae, operating distance of up to one mile, purported 6x signal strength, and support for WEP, WPA2, and WPA-PSK encryption.
There's a less expensive way, and then there's the way that works for you. The two may not be the same.