Hi Ernie, I don't know if you researched Purina yet (?) They do make food for tilapia.
http://www.fishchow.com/aquamaxfishdiets.htm

I don't know if it's the best or cheapest, but my dealer is an 1/8 th of a mile away.
My purina dealer will special order a bag of exactlly what I want. I order ahead of time, they just add it to their regular order.
I was told Tractor Supply is a dealer, but they won't special order.

I think the last bag I ordered was the 500, just over $30 with tax.

You should have a dealer near you. Here is a link where you can find one...
http://www.mazuri.com/usamap.htm