Here's I reasoned myself with the similar problem concerning economy.

I buy Dektol but the idea is the same. 6 dollar bag will give me 1 gallon of stock solution. If I follow the manufacturer's specification for dilution, I use 8 oz + 16 oz water. That means 6 dollars = 1 gallon = 15 tray full. (tray = 8x10 size) Stock solution lasts 6 months per spec. 6 months = 26 weeks. That's more than 1 printing session every other week. I don't print that often. Also, I can spare 6 dollars every 6 months.

What all this means to me is, there is no reason to skimp on developer for economic reasons. If you want to play around with dilution for density control, yes, but it's silly to do that to save few pennies. You'll be far ahead on saving by skipping one Starbucks coffee every other day.

I am not sure which Arista developer you are using but I bet the scale of economy is about the same.

I just follow manufacturer's recommendation.