Take a look at
www.dogfoodanalysis.com
Wellness is listed as a 5 star (out of 6) dog food, which is great! If you take a look at other dog foods in the 5 star category you will find that many of them are cheaper than Wellness. You won't find any foods in the 5 star category that are $20 cheaper than Wellness though, at that price point you will be sacrificing quality. There are a few foods in the 4 star category that are good as well. Look for brands that are made by the same companies as the top foods. Many companies have a top line of foods and a lower line of foods. Acana for example is made by Orijen which is one of the highest quality kibbles out there. There is also Evo (top quality) and Innova which is essentially the step down in the same brand.
I would suggest you take a peek at Acana, it is quite a good food. The grains that are in Acana are high quality grains, and the oils used are fish oils, not vegetable oils so they are actually digestible!
Orijen Adult is about $65 for a 30lb bag, and Acana Adult is about $49 for a 30lb bag. There is also an Acana grain-free line that is about $58 for a 30lb bag.