WSPR transmitter using Raspberry Pi is cheap. The antenna feedline may cost more than the transmitter
This is not your traditional transmitter! The output is essentially a sampled squarewave. There are all the usual odd harmonics, but there are also harmonics that, due to sampling / aliasing can end up very close to the carrier. Spurious outputs will vary, depending on the output frequency.
Receivers can be made using inexpensive Software Defined Radios and cheap computers. Total cost for new gear can be under $150.
A network connection, or a local GPS are required for both the transmitter and receiver. WSPR depends on precisely-timed transmitters and receivers.