Despite the fact that in better neighbourhoods and the city centre have good veggie offerings, the traditional family offering will be meat heavy. If you are with a host family you should let them know well in advance you are vegetarian. The price of vegetables, believe it or not, rises and falls with the tide here. A few weeks ago I paid 45 pesos for a kilo of tomatoes, on saturday I paid 18. So the amount and variety of veg that a typical family will buy changes depending on price and availability.
Staying with a host family sounds like you are going to be dependent on them rather than buying your own food?