- a Si570 generator/kit, at 60€ or so, and it requires a power amplifying chain
- a frequency multiplier
A varactor is a sort of high power varicap diode which is able to return a signal tripled in frequency with a 35% efficiency, all with passive components. FM or CW only. Since I own a 30W UHF transceiver, I potentially have a 10W CW 1296 MHz transmitting chain. I think this technology has been almost forgotten, while today it would allow many amateurs to give 23 cm a try.
A quadriband transceiver will transmit on 70 cm (or at least 2m if using a 5x multiplier), and they are very popular => no additional cost.
An RTLSDR stick will provice wideband 23 cm coverage for 20 USD.
A computer is then needed as part of the receiver, but I would say most HAMs own one => no additional cost.
So, for the cost of a RTLSDR and a varactor multiplier you can be active on 23 cm (CW/WBFM). Not bad.