These fares really exist, but only for a handful of days in each direction. If you don't care when you travel just so long as it's cheap (and you don't care how long you stay particularly) then these bargains might be just the ticket.
In addition to the limited-date $8 fares, there are also $44 and $88 one-way fares (round-trip purchase required) for longer travel periods. These fares can only be purchased on Spirit's site.
This sale ends May 9 (that's today!) at midnight.
See details on Spirit's site.