us.lastminute.com may have some deals for you, but I've heard bad things about them. So, caveat emptor.
ORD is one that would work for you with an 8:30 flight and avoid the need for a car. But the ticket is spendy.
This link from TPA might help you see what flights out are available at or after 8:
http://www.tampaairport.com/flights/index.asp