Right now you can score some super cheap Earth's Best Baby Food at Amazon.com, you can buy it for even less than some gerber baby foods!
I find that making your own baby food is really the cheapest solution, but sometimes you just need to be able to throw a jar in the diaper bag and go. The jars are vacuumed sealed so unlike homemade, you know it won't go bad in your bag or in the car. Plus, when you buy baby products online, you don't have to worry about taking your little angel to the grocery store!
Earth's Best Organic 2nd Fruit Variety Pack, 4-Ounce Jars (Pack of 12) - $8.99