We just returned from Tobago, with two teenage daughters. Highly recommend Ciao Cafe in downtown Scarborough (north of the ferry pier). Really nice Italian Ices and the only coffee worth drinking in Tobago. I believe they offer some Italian dishes in the evening.
Another choice we really liked was the House of Pancakes on Milford Road (toward the airport from Bacolet). Run by a really nice guy named Wayne, superb pancakes and waffles with tropical fruit sides. Go when you have some time, as service isn't always speedy, but well worth the wait.
We found that a nice dinner for four with drinks and dessert ran about $600-700 TT. A quick meal from a takeout place (Pizza Boys, Chef's BBQ) is considerably cheaper, around $100 TT or so.