How small are you looking to go? I wouldn't really do anything less than twenty gallons ish. You could do comb jellies in that. Honestly, if you're looking for cheap and easy, I would just skip jellies. In my opinion, they're kind of boring. We have two tanks made right now. One for use with a canister filter and one for use with a sump. The canister filter one is easiest in my opinion. What we did was cut out a circular tube, siliconed it in the tank. There's a six by twelve inch rectangle cut out of that. Cover that with screening, I just used the stuff from Lowes. Place one end of the cut out cylinder higher than the other, so that when you push the water through it goes into the cylinder and not into the rest of the tank. Put the intake on your filter on the side that the screen is on. Then on the other side put your output with the sprayer bar across the cylinder so that when the water is pushed into the tank it will spray in. On one of my tanks the sprayer bar is siliconed in, on the other the bar is suction cupped on. If you are going to collect the jellies yourself, I just recommend using the water that you collect the jellies in. Since you're on the gulf you should be able to find some combs. I used to see them all the time in Texas, and I'm even getting them up here in Jersey. If you have any more questions, or need a diagram or something, let me know.