One thing to keep in mind is that a cat needs to eat less of a good quality food because it is more nutrient dense, doesn't have cheap fillers. A cat eating a dry food diet (not a good thing, but it doesn't seem to be the time for you to make a switch to wet) of a good quality food only needs 3/8 to 1/2 cup per day (which I would split into 2 or 3 meals). A cat eating a poor quality food needs more like 3/4-1 cup per day. So keep that in mind when you assess prices. 6 lbs of a good food is like 10-12 lbs of a not so good food.
A good quality food for a reasonable price is Natural Balance which you can get at Petco or local pet shops.

Value
Costs less than other premium cat foods. Pound for pound, Natural Balance Original Ultra costs less than California Natural Chicken and Brown Rice Formula (*Est. $15 for a 5-lb. bag), another premium dry cat food with grain that gets ѕimilar reviews.
Natural Balance costs more than supermarket dry cat food, but several cat owners who write reviews at Amazon.com say their cats have eaten less since they switched to the more nutrient-dense Natural Balance.
The bottom line
Although some top experts say grain-free or canned cat food is better for cats' health, Natural Balance Original Ultra gets good reviews and costs less, making it a top value among premium dry cat foods.