Check out restaurant.com to see if any of the restaurants in Tybee or Savannah on listed on their site. They are running a special for $25 certificates only $2. Sorry, I'm not sure when it ends, but I THINK the promo code is FLAG (there is a restaurant.com thread in this same boards section that can confirm code/expiration date). If you are not familiar with this site, please make sure you read the terms which appear when you click on the dollar amount of the certificate (i.e.- minimum diners, minimum purchase, alcohol included or not, one per party, etc.).
Another site you may want to look at is SavannahMenu.com which offers a VIP card for a price. It has been almost 4 years since we used that, so can't offer any other current information other than they are there if you want to check them out.
Check out the Visitor's Center on MLK to see what type of coupons you may find. We did the trolley tour when we visited, taking note of what we wanted to revisit later to check out further.
What I enjoyed when we visited almost 4 years ago -
Breakfast at Clary's Cafe (original location in/near Historic District)
Lunch at Mrs. Wilke's Boarding House (closed weekends, but if there during the week, really a not to miss)
Some disagree, but we enjoyed a dinner at Lady & Sons. Not only that, we got in without reservations because we said we would eat upstairs (bar area), though they ended up putting us at a window table instead, one floor below.
We didn't do the carriage tour in Savannah, but I felt sorry for the horses because some of those streets are very steep. We saved that type tour for Charleston which was awesome.
The one place I WOULDN'T recommend anyone miss is visiting the Cathedral of St. John The Baptist. It is an absolutely stunning church and shouldn't be passed by without seeing the inside.
While on Tybee we had a late lunch/early dinner at StingRays where we enjoyed the food completely and the service for the most part (they were swamped and the hostess was enough to make me turn around without entering). Personally, I would completely avoid The Crab Shack on Tybee. I've posted reviews on Trip Advisor for both of these restaurants where I also go by HMin. But again, keep in mind that it has been almost 4 years since we visited some of these places. We were there less than 2 years ago, but ended up cutting our stay short so I really can't offer any later input other than Clary's which I still loved!