South Beach on student budget
Here are some older threads on cheap eats in South Beach (I stopped bookmarking these at some point); some of the info is still accurate but check and update, some places mentioned (Dogma, Le Bon) have closed ->
Budget priced Asian food is not exactly South Beach's strong suit, but it rarely is in any high-rent tourist destination, plus the greater Miami area is generally weak on Thai and Vietnamese places. Rather, you're better off focusing on the cuisines that are closer to home here - Tap Tap (Haitian) is a good suggestion, or Cuban (Puerto Sagua, David's Cafe), Peruvian (Chalan), Argentinian (Baire's Grill) ... though Indomania (Dutch-Indonesian) is a great place that cuts against that line of thinking. Entrees are mostly under $20, and the rijstaafel (for $24 or $28 per person) brings a huge assortment of food and a lot of fun.
I like The Spot on Alton Road for their fried shrimp po'boy. I also had a perfectly decent steak-n-cheese sub at the Alibi, which is tucked away in a bar called Lost Weekend on the eastern end of Espanola Way.
South Beach is weak on Asian food and Asian places on Lincoln Rd. are very subpar. If you want something cheap and authentic try Tap Tap on Washington. Good Haitian food with extremely good mojitos (one of the few places where Miamians actually order mojitos). Then go to Lincoln to Zekes or Segafreddo for drinks if you wnat to peoplewatch.