A GMRS Small Base Station can already do this, at least on the first 7 shared FRS/GMRS channels.
You're allowed 5 watts ERP on those 7 shared channels, with a 20' height limit above ground (if the antenna is mounted on a ground mounted tower), or 20' above the structure on which it is mounted, such as the roof of your home.
All you'd need is a handheld radio, or a low power mobile radio (Midland produces both 5 watt and 15 watt GMRS mobile radios with channels 1-7 and 15-22), low loss coax, and a unity gain (quarter wave) or low gain antenna.
Remember, ERP is figured out by taking the power output of the radio, minus the loss in the coax in dB, plus the gain of the antenna in dB. A 10 watt radio feeding a quarter wave antenna with coax that has 3dB of loss will give you 5 watts ERP.
And I have 2 of those Radio Shack mobile FRS radios.
John
WPXJ598
Peoria, AZ