For this one, you need to book by May 26 for travel, with some exceptions, through Nov. 10. Best prices are available Tuesdays and Wednesdays. This requires a 10-day advance purchase, and there are blackout dates and other restrictions. Here is the fine print, and some sample one-way fares from Boston.
Baltimore $54; Milwaukee $79; Atlanta and Newport News/Williamsburg $84; Raleigh/Durham $89; Akron/Canton, Dayton, Fort Lauderdale, Indianapolis, Jacksonville, Memphis, Richmond, Pensacola/Gulf Coast, Sarasota/Bradenton, Tampa, and West Palm Beach $94; Flint, Fort Myers, Grand Rapids, and Miami $99; Charlotte, Columbus, Dallas/Ft. Worth, Bloomington/Normal, Minneapolis/St. Paul, Orlando, San Antonio, and Houston (Hobby) $104; New Orleans $105; Bermuda $109; ; Kansas City $113; Wichita and Detroit $114; Cancun and Rochester $119; Branson $129; Key West $134; Huntsville $144; Aruba and Omaha $149; Las Vegas. Seattle, San Francisco, and Los Angeles (LAX) $154; Des Moines $159