I made this recipe for lunch today:
http://www.eatingwell.com/recipes/tijuana_torta.html

It was quite tasty! They are basically black bean and guacamole sandwiches and I came across the link via an article on Yahoo about cheap meals for under a certain price. Any recipe involving beans is usually relatively low cost.

If I make them again, I'll probably add some cheese to the recipe (a nice Monterrey Jack or Mexican Cheddar) and cut the lime juice by a little.

Enjoy!