I'll start. I feed pellets, primarily, and shrimp/snails/superworms as treats.
I believe pellets meet all of the requirements except "low cost". Hikari Massivore is found cheapest when bought in bulk (2.2 lb bags) at $18/lb. Hikari Sturgeon is cheaper, but still high at $10.50/lb.
I am looking for a cheaper alternative. Plus, many times it proves extremely difficult to convert rays to pellets.
may i ask where did you get 2.2lb massivore sale at $18 ? i need those my ray and pbass killing me with the food bill LOL