I'd advise to use only high quality pellets, not the ones based on wheat, beans, corn and Co. Something that costs at least $5+ per pound. From personal experience.
The cheapest and effective nutrition is baitfish, f/w or s/w, whatever you can find. Whole, head, guts and all is the best of course (fillets are just protein, no vitamins, minerals, trace elements, gut content (algae for instance), enzymes, co-factors, etc). Frozen. Usually can find at $1 per lb. Presoak in VitaChem supplement solution.
I use s/w baitfish. Some are concerned with the salt content. I can't say I've arrived at any indication that it is a problem for our f/w predatory catfish and Co. If that worried, can soak the salt out in tap water before VitaChem soak. Or find a source of f/w baitfish.
Baitfish is often found at angling shops and can be found at wholesale places at the quoted $1/lb, like herring, pilchard, shad, mullet, glass minnow, anchovy, etc. etc. etc. From retail shops the price will rise to $2/lb or more. Still better than $4/lb human grade food tilapia fillet.