Check comparison websites that will search several travel businesses to find you the best rate. KAYAK.com, among others, searches databases for hundreds of sites for the lowest fares. You can also find hotels, cars, and vacation packages on the site.
Trip Advisor allows you to compare flights also, as well as sign up for alerts when prices change from your city to Myrtle Beach. The site also outlines popular attractions, aggregates recent deals travelers have found, and lists reviews of airlines with service to Myrtle Beach.