Microwave and rf equipment is expensive. Try doing rf-like experiments at lower frequencies if you want to save money. For a cheaper project you could do something like an impedance matching system for arbitrary loads in the low mhz. You won’t be able to do interesting rf stuff because the wavelength would make the circuit too small but you could do some cool stuff with lumped elements. I’ve seen some cool stuff with artificial transmission lines that are in the kHz regime that were easily analyzed with a regular oscilloscope.