Here's a good site that details a homemade rat food dite, so if you look at this you will get an idea of what needs to go into a good dite for your rats. Also it details some other information about nutrition.
Just because that is the only one that sells in bulk in your area doesn't mean you can't contact the food places themselves, and get it bulk direct from the supplier. In some cases this is even cheaper then buying bulk from pet stores or other places like it...here is some information from ratsrule.com about some other options for feeding your rats.
â€¢ Harlan Teklad www.harlan.com
PO Box 44220, Madison, WI 53744-4220
Product - #8604 Rodent Diet (soy-based)
Retail - Available from the RMCA and Rat-Store.com
â€¢ L/M Animal Farms
10279 State Route 132, Pleasant Plain, OH 45162
Product - Square Meal for rodents
Retail - Available from Ritzy Rats Pet Shop
This is the brand I have had the most luck with, personally.
Other lab blocks available via retail:
â€¢ 8-1 Plus Advanced Nutrition Diet for Rats & Mice
I have never tried this brand, so I can't comment.
Hope this helps you out, and that you can tell your parents to maybe get your rats on better food.