this VNA is super great. for $600 you get up to 8Ghz (not a typo, 8GHz can be archived in harmonic mode) usable range. with two of them you can do 4port measure

this VNA is super great. for $600 you get up to 8Ghz (not a typo, 8GHz can be archived in harmonic mode) usable range. with two of them you can do 4port measurement. you can also produce time domain reflectometry with it. open source hardware, firmware, fpga and pc side software.