Crystal, Hello . I'm afraid I don't know any caterers who would be willing to do a dinner for $42.00 usd a head (actually buffet is more expensive than sit-down as more food is involved . You might try a place called "Karen's Place" in Bucerias - it's a little restaurant on the beach - I don't know what her pricing is, but a restaurant might be more willing to work with you on a limited budget. If you can raise your budget somewhat, you might also try DeSantos - again you would need to have the wedding at the restaurant in order to keep the costs low, but it's a beautiful space. I doubt you could get something for $42.00 usd a person but they might go for something a big higher - it would just be a matter of writing to them and see .
I didn't know there was a Ztai in Bucerias - the only one I know of is in downtown Vallarta. If they have a place in Bucerias then I say go for it - their food (in the downtown location) is pretty good .