We have looked at these types of transistors before. I picked up one of these for $104: http://tinyurl.com/h568esp
If they were available mounted on a finished board that only required soldering power leads, heat sink, and plugging in the coax, that would be even better!
Very soon the manufacturers of LDMOS transistors will be offering a full board, including also the frequency generator capable of being computer controlled in phase and frequency:
These are cool. NOT. They are specified as fairly narrow band devices, to comply with ISM standards when mounted on the board (i.e., you're almost, but not quite, tuning the frustum to the source). They require tens of amps of clean direct current (beware of Lorentz forces). Their efficiency is comparable to a magnetron, so expect to shed several HUNDRED watts of heat. A magnetron is a vacuum tube, and tolerates the heat. A solid state transistor, whether LDMOS like this one or GaN like the Macom device, nah, not so much. These devices are presented on evaluation boards optimized for a 50 ohm source and load for evaluation purposes. A frustum is not a 50 ohm load. S-parameters are strictly for linear purposes normalized to the network impedance. Beware S-parameters for non-linear devices launched into non-normalized conditions. Finally, these are amplifiers, not oscillators. They have a certain gain, at a certain frequency. You still have to drive them with a source of somewhere on the order of 4 watts of microwave RF. Keep in mind that the microstrip design of these protoboards radiates an E field quite well.
Be safe. If you buy one of these devices, and build one of these amplifiers, and don't enclose it in a well shielded RF tight enclosure, you can expect to wake up the next morning with eyeballs that look like poached eggs. Forever. As a test, over-ride the interlocks on your microwave oven, stick your head inside, and turn it on medium for one minute. Don't do this. But do contemplate the result.
A magnetron power supply will kill you, no questions asked, right now and right away just from the voltages and currents involved. A high power RF transistor may not shock you to death instantly, but will do so insidiously, and it most certainly can cook you or burn you to death. Or put you into a condition where you wished you were dead.