Any website for very cheap tiks
try Orbitz,kayak,travelocity I like orbitz since they will put say a DL there and a AA back as 1 tkt usually under Multi Carriers, also if you click to, they will say have you leaving EWR and back into LGA. if you arent parking a car at at the airport this may work out
the same for your destination which if FL isnt too bad as most Car comps dont have a drop off fee in FL. Most any where else the drop off fee can be more then the rental itself
so for a NY area flight Check LGA,JFK,EWR,HPN (very costly parking and limited),SWF and even PHL but befoer jumping at the cheapest work out what it mau cost in gas,tools and parking as they can very easily off set any savings on the fare itself and make it more expensive in the end. If I can park for free at say LGA or JFK or get someone to drop me and pick me up then it doesnt pay for me to save say $30 and go via PHL. As it will cost me more then my savings. If I was going to park at LGA which is over $20 a day then PHL is OK as I can park there for $6-8 a day
also check into alternative airports for where you heading so if FL, PBI,FLL, and MIA for Southern FL. For Orlando Id look at TPA,MCO,MEL(limited service) or JAX and where a car will be the cheapest . no sense flying into PBI and saving say $20 if you spilt of teh car will be say $35 more then if you went into FLL
Unfortuantely there is no simple way to work it all out but by trail and error, it will be time consuming and might gte on your nerves or to those of us who enjoy it its all part of the Game
But do get out of your head that you will find something for under $100