The above suggestion may be least expensive, but I don't like the idea of bleach and dish soap. (not hating) I use H202 and (2) 20 gal trash cans. I let it all simmer in one can and then dump it over to the second can a few days later and go back and forth. Its a pain
I wish I had more room and I could build a nice station for it with some screens. I know you can also use enzymes, but that would be even more expensive. No matter what the situation, I find that H202 works great to clean hydro set ups. I use the 30% and a little goes a long way