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I have used WiFi boosters as amps for ATV, they come in all shapes and sizes but they can do upto a few Watts for a 10mW input.
They need some mods to make them suitable for ATV though as the PA device isusually not heatsinked enough for 100% duty cycle. You can get these on ebay for as little at £20 for 1Watt or more.
If you are looking for some reasonable power the Spectrian driver amps are quite good for 30Watts on 13cm, they need ~10mW of drive and a big heatsink, they often come on ebay from the states for ~£100, remember there's import tax to pay on them!
The big Andrews/Remec amplifiers also come up very cheaply on ebay and would give you ~100W on 13cm for ~£35 but they are very power supply hungry about 10A at 48V!
Saying that you could just remove the driver board from these and use that to get a watt or two.
Minikits in Australia probably do some 13cm amp kits.
I'l leave it for others comment on any ready to go bits of equipment if you are not upto modifying anything...