This is a great tank. There are so many options for the 20g long. Since you're apparently not planning on doing any SPS, you don't necessarily need metal halides, although I've found I end up spending more money in the long run by trying to save money and get equipment that only meets my current specifications. But, as with anyone, my preferences change, and so do my equipment requirements.
Understanding, however, that price is always a factor, you could definitely go with a Current PC setup. Your frogspawn and torch corals (any stony corals, really) ought to have at least T5s, but those two will still be OK under PCs, they just won't thrive as well as they could. I used to have a Current Satellite 65w fixture over mine before I decided to upgrade to metal halides.
Your best bet is to try to find used or build a fixture yourself. If you have the time, you can very easily build a hood for this tank with two 70w metal halide fixtures for under $100. That's what I have over my tank, and it's the best investment of time and money I've put into my tank.
All that being said, try to determine what your current financial/time requirements are and what your future preferences might be. If you think you'll only stay with zoas and frogspawn, PCs are just fine, but T5s would be ideal. If you ever want to dabble in some harder corals with higher lighting requirements, go for metal halides, you won't regret it.
