Donna,
Donna,
the problem with running these kinds of discounts or specials is that it always leads to an increase in the "leaky bucket syndrome" --poor customer retention. The type of customer that these offers appeal to are not the type that remain loyal. In fact, all market research has shown, again and again, that these kinds of customers have no loyalty to brand or location, but to price, and will move on if someone else nearby has a better "deal".
If you are the only game in town, then that's even more reason not to offer this kind of special. It will do nothing to grow your customer base. It will only amount to spot increases in sales. You need to look at each offering you make as an indication of how you view, and how you want the customer base to view, your entire operation. You need to see the long term picture, and understand how this will positively or negatively affect you down the road, or even in the near term positioning of your business.
My cent.