You've definitely got a multitude of combinations in pump styles and diffusers. From rotary vein to linear diaphragm pumps. Air stones to rubber membrane diffusers. The cost of each dependent on their individual sizes. Your budget will ultimately determine which way you go.

Knowing your max depth, as stated above, will dictate what size pump you need. Diffusers should be of a type that will give you the maximum lift you can get, which is typically a rubber membrane type with tiny holes that create thousands, if not millions of tiny bubbles. The more bubbles the better as this creates optimum lift, thus creating enough current to turn your water over (at least once every 24 hours). For every foot of depth, you're looking at .5 pounds of pressure, so if your diffuser is 10 feet deep, your pump needs to create a minimum of 5psi.

I personally went with a linear diaphragm pump that is rated to 20 feet. The diffuser setup is tubular rubber diaphragm arranged at 9 foot deep. With the included 30 feet of sinking 3/8" airline, my complete cost was under $600. My pond is small (187,000 gallons), but we've estimated this kit turns the pond over at least twice in 6 hours.

Knowing the depth and acre feet of water will get you going in the right direction.

.10 surface acre pond, 10.5 foot deep. SW LA. The epitome of a mutt pond. BG, LMB, GSF, RES, BH, Warmouth, Longear Sunfish, Gambusia,Mud Minnows, Crappie, and now shiners!!...I subscribe!!