For one, cut your costs by using smaller pumps, one to control each level. That drastically drops pump cost.

Instead of individual sprayers, get a sprayer hose line, drill 1/64" holes in it. Clip it down. Less clog, pretty much the exact same spray.

Dunno where you're finding the PVC tubing (I know Home Depot doesn't carry 4" typically in any useful length for this kind of system,) but I am quite sure you can find it cheaper elsewhere, though you might have to wait on a lead time. Most global manufacturers can do direct for cheap if you can order by the container load.

4-way PVC joints and the two-sided end fittings for closing the end of the ring can be found at varying prices depending upon quantity ordered. Buying in large stock as if you were planning on selling these out will drop your prices and allow you to sell more.

Just sayin from experience, from helping to run a Chinese restaurant to running this business, when you want quantity sold, you need quantity bought, and then more.