You CAN go to lunch for less than $10-15 - just depends on where you go and what you order.
I'm not current on my specials at local restaurants (I bring my lunch rather than eating out due to the economy) but there are places all over 30-A that are not only reasonably priced, but feature daily specials and local's discounts - making them a much better deal and a much better meal than Taco Hell or McDonald's.
Flip Flops, Hurricane, Fire, Publix, Coffee House, Don Pablo's, Jambone, Village Market etc.
Modica's posts their lunch specials on Sowal, Bruno's used to have pizza, salad, bev for $6, Amore had a drink, GOOD salad, and half a pizza for $8 ....
Not saying some places prices aren't a bit high, but there ARE quite a few options.