Just thought I'd throw out there that one of the Acana formulas, Wild Prairie, might actually be in your price range - the store I work at sells the 29.7# bags for $54.
It's pretty nutrient dense too so I'd expect your portion sizes to be smaller (therefore the food lasts longer), but it's not SO rich like Orijen is, which can be problematic for some dogs.
I'd also look into Go! and Now! Natural but I honestly can't remember how much we charge for those, so they might be well out of the price range.
I like Fromm as a company, as a whole - they make good foods and are a trustworthy company. Their grain-free formulas come in 26# bags and run upwards of $55-$60 depending on the flavor. Their formulas that include grain come in 30# bags and I'm kind of blanking on the price... but I'm pretty positive they're less than $55.