I think everyone feeds their rays and fish way too much. HERE IS MY STOCK LIST!
I have 12 rays, 18" Mbu puffer,18" Armatus,two 22" black arowanas,2 adult Lenticulata pike,13" ID shark, 7" Black wolf fish,13" Arimara wolf fish, 7" Geryi piranha, 9" Black Diamond rhom,7" marbled goby,21" Tigrinus catfish,two 6" Hydrolycus tatauaia,two 5" clown loaches,5" striped raphael , two 3" spotted raphael and a 18" Aba knife fish.
My cost a month in food is probably only $65.MY STAPLE IS SMELTS! I get 11 lb boxes of smelts for $30 and 2lbs of raw shrimp for $12. Then I have some shelled seafood for my Mbu puffer. A box of smelts last at least a month and I use probably about 2 1/2 bags of shrimp. I only drop some massivore pellets once a week to the rays and feed some pellets to the clown loaches and ID shark. My rays are breeding and have had pups and all my other fish are growing. All my tanks get starved at least once a week, except the tank with the pregnant stingrays.
My tanks only get the water changed once a week with the exception of my 450 gallon with the adult rays. It gets changed about every 5 to 6 days. Depending on how much I fed them during the week.
My only real big cost is the power bill, which usually is around $400/month. Water is about $150 and my food bill is $65. So as you can see it's the utilities that kills me not the food. Just cut back on the feeding of your rays and they will be fine. The result will be a cheaper food bill,happy healthy fish and better water quality.