Cheap and very good just don't come in the same package whatever you are buying. However I think the Maximum range of modulators are very good and reasonably priced. The MT47 covers VHF and UHF and can operate in systems B/G, I, D/K, L, M, and N. The MT57 is similar and can produce Zweiton Stereo on system B/G. Both are double side band and I seem to recall are around the £35 mark.
https://uk.eetgroup.com/i/4320-Maxim...specifications