Get thee to a Ham rally, what you want is a "Radio comms test set", even something like an Anritsu 8801B would do, and I got one of those for £60 (Screen is poor, a common failing on that model, but replacements are allegedly available).
They usually (these days) come designed for mobile phone testing, but a few button pushes will usually get you to a useful spectrum analyser, power meter, and often a signal generator. Because they do not usually say "Spectrum analyser" on the box they go for little money considering that the original price was usually 5 figures.
I would suggest however that what you really need for antenna work is more likely to be a VNA, somewhat rarer at a reasonable price point.
73 Dan.