I am looking to get an edgerouter in the future. This would probably do exactly what you are looking for. It is based on the "Vyatta " software. Note you will need some knowledge on how to set it up. They just released them and they are hard to get. Current price is $99.
Datasheet: »www.ubnt.com/downloads/datasheet ··· e_DS.pdf
»www.ubnt.com/download#doc:EdgeRo ··· ter:Lite
»forum.ubnt.com/forumdisplay.php? ··· 1a1&f=84