Biggest adventure of the year-plz help me get it off the ground!

Alright, heres the story, My name is Ross, I'm 18 and I live in Northen Ireland(that UK to all you american-no offense).
For my summer holidays(vacation) i really want to travel round some of America-therefore a road trip would be ideal! Flights i can deal with but my question is about the car rental(would just be way to expenive due to insurance becasue of my age or what)
-and to really live the film- ne chance of a big open top pink cadalac(soz-cant spell that)??Ideally id live to get somesort of job for maybe 3or 4 weeks while im there- to help pay for petrol(gas) for the rest of the time(another 3 or 4weeks)
Can ne1 help?All suggestions welcome.Oh i do have a few american contacts-one in chattanooga,TN and i think one in orlando!Thanks for any input-ross

Ross,

I'm sorry, but I'm fairly sure that most car hire companies in the USA will not hire to people under 21. From 21 to 25 you have to pay a hefty supplement. Check it out yourself rather than just take my word for it.

Its everybodies dream to hire a convertible but I'm afraid they will usually cost a good 50% more than an economy car.

You really need to get an older friend to go with you which is not what you probably wanted to know - sorry.