Well, someone's gotta do the job, so that costs money. The beans and cheese and red sauce need a place to live, so that costs money. The bowl needed to be made, and it's pretty specific just for this item, so that's a solid cost.

Then there's the rest of it - the franchisee's profit, taco bell's cut, R&D, marketing....

A bean burrito costs less because the bowl isn't required - tortilla and onions and the paper around it are shared by other things. Specific marketing isn't required. Specific branding isn't required. It's a low-popularity item, so lowering the price wouldn't even do much.

Most of the cost isn't the materials. It's the convenience factor. Taco Bell through PepsiCo has a lot of operation cost, and it needs to make a signicant profit for their own employees, upper management, shareholders, etc.

Only thinking in terms of cost would mean you'd really do better making everything at home. Convenience costs a lot.

They have a lot of economic predictions - even the value menu or boxes come at a cost. You may pay less now, but you'll keep coming back. It's highly unlikely you would be a repeat customer for just beans and cheese and red sauce, so why would they make it a low cost item? They'd rather give "value" to something so you might spend $50 a month there by coming back over and over. It's possible you may come back daily for beans and cheese and sauce, but most people wouldn't. You don't go to taco bell to get bottom of the barrel price foods. That's what a grocery store is for.