Have you thought about using a micro-jet 320 powerhead? You can find them for less than 20 bucks online. You can could use a Dremel (starting at around $40 at most hardware stores) to drill a small hole in one size just large enough for the nozzle and drill a couple of holes slightly smaller than that on one of the opposite sides. You should be able to get a sheet of plexiglass at Home Depot or Loews to cover the top, and you could glue the powerhead to the side for stability. Those powerheads range from 32 to 73 gal
. per hour, so you could probably experiment with the rate and get good results.