There's no need for anyone on a budget to go hungry in Puerto Rico. The least expensive places to get a great meal are the roadside stands which offer a variety of local fare. For those who are leery of eating at establishments such as these, there's always the deli at the Pueblo or Grande Supermarkets. The food is fresh, cheap, and tastes as good as the expensive restaurants.  A very popular and moderately priced restaurant is the Metropol in Isla Verde. There are also all the regular fast food chains as in the States. At the airport and many of the hotels you can pick up a dining guide which rates the local restaurant costs by using the dollar sign code - one $ sign for the least expensive and $$$$ signs for the pricey places. The malls have food courts too. The restaurants at the hotels tend to be expensive and you don't get the flavor of the island which you would experience at the local restaurants. 

For breakfast, visit the local panaderias.  They have an impressive variety of sandwiches, pastries, and delicious coffee.  The quesito, a sugary cream cheese filled puff pastry, is not to be missed.  If you are off to explore, it is a good idea to pick up a sandwich to take with you later.  Panaderias in the Condado area include Kasalta and the bakery at what was formerly, Pueblo supermarket on Calle de Diego.  It is closed for renovations under new managment and will reopen in the summer of 2008. In Isla Verde, try España.  A good local chain for sandwiches is El Meson - kicks Subway's patootie every time.  For lunch, go with the locals' advice and try places such as La Fonda del Jibarito and Manolin in Old San Juan and Bebo's in Condado.  Most small hole-in-the-wall restaurants have lunch specials not to be missed if you want to make lunch the main meal of the day.