There are several restaurants in Sebastian and Vero Beach (for those that are unaware, you are just as close to Sebastian as to Vero when staying there) that are listed on Restaurant.com (April 5-10, the 70% off at check-out PROMO Code is: PLATE) I know that Capt. Hiram's is listed, as is Mo-Bay Grill in Sebastian, and Riverside Cafe in Vero. There are several others, but these come to mind, since I've recently purchased a few.
i.e. You can purchase a $25 gift certificate for about $10-$20, so with the Promo Code, it would be $3-$6. These would require a minimum $35 purchase at the restaurant, plus an automatic 18% tip on the entire purchase (I usually leave about 18% anyway, so it saves me the time of figuring it up). On every certificate I've purchased, there is no expiration date, however you are limited to using only one certificate, per restaurant, per month, so you probably shouldn't get more than 1 for each restaurant that you are interested in for your visit. I'm not sure if it means calendar month or 30 days (You may possibly be allowed to use one at the end of one month and then again at the beginning of the next--not sure). We ate at Riverside Cafe last month and saw country singer, Jake Owen (born in Vero Beach) there. Capt. Hirams has a sand bar, with inside and outside seating along the Indian River. I haven't been to Mo-Bay Grill yet, but it is highly rated, #3 in Sebastian on Trip Advisor, and 4-star in Florida Today, so I have high hopes.
Also, as OKWJan pointed out, there is a new Mulligan's in Sebastian along the river, and one in Vero at the ocean. They are not on Restaurant.com.
Hope this helps someone save some $$.