Use a tunnel diode circuit. Finding tunnel diodes these days is difficult, however. But time domain reflectometers often used TDs for their picosecond-area pulse generators, e.g., the Tektronix 1502. However, the higher-power TD used in the 1502 even back in 1979 when the 1502 was in its heyday ran around $150 and went up to around $500 around 1982. But smaller TDs (GE was a major supplier for Tektronix) used in the triggering circuit of Tek scopes such as the 465, 475 and 485 weren't so bad.
Tunnel diodes, the darling of the electronics industry from around 1967 through around 1982 were also used for UHF oscillators.
Dean