Regardless of pricing, you should consider switching to rubber membrane diffusers. They put out smaller bubbles than stones and are more efficient at raising and circulating water.
Uh oh I'm going to play devils advocate here again. There is at least one time you should use stones over membrane diffusers. At least from my experience. That's when you're using one of those diaphragm compressors that pumps out less than 1 cfm.
I use two of them now on my two ponds that have fish for the winter for winterkill prevention, and I don't want or need a lot of flow. Just enough to keep some ice open. I change out my rotary vanes for the diaphragms in the winter now for that reason. It also saves on electricity use as the diaphragms use a less electricity than the rotary vanes due to fact that are much smaller in hp.
I find I don't get much air out of the membrane diffusers at less than 1 cfm. I also use only one stone.
In fact, I made the mistake of leaving a membrane diffuser on my airline in a pond this year when I changed out the rotary for a diaphragm. I couldn't get any air to come to the surface to speak of. It was a pain, but fortunately I had a rope connected to the end of the airline and once I pulled the airline up and changed out to a stone, I was able to pull it back under the ice with a rope from the other side of the pond. Always learning!
