[DonRotolo]

33 kHz is high audio, and the 555 timer will happily do that all day. Without a power supply, I could do that in less than 1 cubic inch. About $2 at Radio Shack, add another $8 for resistors, capacitors and maybe a circuit board.

While not exactly a precision frequency system, a 555 can be held to reasonably close tolerances by managing temperature.