probably more time/cost-effective to grab one of those cheapies off ebay.
While you're at it, go ahead and grab one of those FCC licenses to go
with it.
(Assuming you're in the US.)
It's illegal to operate at those power levels without a license.
(Technically, the FCC Part-15 limits are specified in terms of field
strength, but you'd have to have a really shitty antenna system at 15
watts to pass that spec.)