Ambergris Caye is a resort, for all intents and purposes, and the prices are the same that one would expect in a resort. Not cheap, for the most part. There are some reasonably priced meals to be had on island, but the majority of the selections are high priced. That's the reality of the situation.
There was a time when San Pedro Town was okay for prices, even though it was at the high end of Belize, which was in turn at the high end of Central America. Now, it's no longer "okay", it's plain expensive.
Sure, you can eat street from the vendor's carts and save a few dollars. You can grab a 1/2 fried chicken at the chinese joint near the post office for BZ$8 or so. They have cold beer at reasonable prices, too. Compared to other places on the island, these are examples of less expensive alternatives.
There are still quite a few places that sell tacos for BZ$1 or so. I think that the bakery has some good offerings for sweet breads that make for a reasonably priced breakfast, especially with a cold glass of fresh squeezed orange juice. However, sometimes you just have to realize that you're in a suburb of Cancun and endure the prices.
I misspent my youth in the southwest and I like the cooking. My granny was born in the Territory of New Mexico and was trilingual, speaking spanish, english and dine. When I was a kid, the best way to spend time with the girls in my neighborhood was to help in the kitchen, and I learned to like home cooked mexican food.
On the mainland I enjoy good food on the cheap. In San Pedro Town I eat local food which is okay and high priced. At least a few times per trip I get a really expensive meal, such as a steak at the Blue Water. It's good and it's pricey, but every now and then a fellow wants a nice slab-o-meat.
On the board everybody makes a stink about the burritos at one of the stands on Middle Street. They're okay. I often have one myself. But they're only fair compared to the food at places I normally eat at in the USA, such as Los Dos Molinos
. I still mourn the passing of one of my favorite mexican restaurants in LA, which was burned to the ground during the Rodney King riots, but there are many like it where I can get a bigger & better burro than at the stand on Middle Street while paying less.
I like good seafood. I made my living cooking in the Pacific Northwest, and I fed the Mayor of Portland, as well as the Governor of Oregon. I run around with a girl in New England and we tramp around the coastal joints in New Hampshire & Maine. Now, there's some good eats up that way, and sometimes you can get quite reasonable prices. For example, I had lobster claws and chowder for $15 back in July. In San Pedro Town, you can get good food, but you'll pay resort prices. I'm not crying about it, but that's the way it is.
Overall,it's important to have realistic expectations of the food in San Pedro Town. It's often quite good, but it's rarely inexpensive.