I went back to Travelocity this morning and the $98.00 Delta flight is gone. The next cheapest flight is out of Providence. It is for $129 + taxes. As of this morning there were seats available pretty much every Monday thru Thursday from the beginning of April thru the end of May - Memorial day is not available. Not sure where you live on the Cape, but we always park at Thrifty Rent a Car down the street from the airport for about $45/week.
The Delta out of Boston now is up to $136 + tax. Looks like these seats are only for the weekends.
Hope this helps. I would check first thing. These prices seem to change quickly.