The best two places I ate and were VERY VERY affordable were:
1) Waruguma - little hole in the wall on middle street, easy to miss, looks like a blue counter stuck between to building with a roof. The owner Ernest catches the fish fresh daily. 3 tacos are $1BZ, fish burrito(which I highly recommend) $2BZ, etc... has one small plastic table out front
2)Papi's diner - this one is further in town have a cab take you the first time because it is easy to drive past. If you drive on your own, it is at the far end of town towards the small channel crossing. Anything here is good. our favorites were the fish fingers and skewer dinners. And he makes a great rum & coke! has tables outside and inside.
And the best part of both of the places is the hospitality of the owners.