A jellyfish tank can maybe be done on the cheap via a special trick: air pumps! Do a
deep sand bed of sugar-fine sand for the
nitrogen cycle, then but put air diffusers in all of the corners. The bubbles will have the effect of slowly circulating the tank and keep the jellyfish from getting stuck in a corner. You have to avoid and strong directional flow, so if you have an overflow to pull out waste, make it cover as much of the whole back of the tank as you can and make sure your return comes out of as many openings as possible, from all sides of the tank and pointing to the center.
I have not done this, but I've seen a schematic of such a tank.