Retail, a 100 count cup of mealworms is about $2, 50 count cup of waxworms is about $5, and crickets are 5-7 cents each. With only one or two geckos, a 100 count cup of mealworms will last you about 3 weeks. Waxworms and crickets can be given intermittently.
Also, you need to figure in the cost of calcium/vitamin/mineral supplements. A small bottle or jar will be 5-12 dollars but will last several months.
You can order mealworms, crickets, etc. online but with only one or two leos, it doesn't make much sense to buy in such large quantities.
To reduce your expenses, you can easily breed your own mealworms. Just put a couple hundred mealworms in a batch of bedding. Oatmeal (non-quick rolled oats), powdered milk, rice and barley baby cerial, etc. all make good bedding material. I always use a combination to give them some variety. You'll also need to put a sliver of carrot, potatoe, apple, etc. in to provide some moisture.
The mealworms will turn into beetles and the beetles will lay a couple hundred eggs per female. In a week or two, you'll start to see tiny mealworms in your box.
If you need more information about mealworm breeding, there are instructions all over the internet. Good luck!!