I don't think I or anyone can tell you how to spend your money, If you have a passion for a Hellcat and can make the payments, more power to you.
When I was 18 ( about 100 years ago ) I think I was making $5.50 an hour but purchased a set of B&W home audio speakers and paid $2,500 for them. My friends and family thought I was crazy but now I am a sound tech and own a audio company so people cant tell you whats right for you.
I do know the satisfaction of NO car payment but sometime you got to pay to play! I also know way back when, all my 18 year old friends destroyed their credit early on with car payments and were never able to buy houses and such until early 30's because of stupid stuff done young. Do understand taking on a big car payment may keep you from buying a house etc depending on your income.
1st, I would suggest use an actual vin# and call your insurance person and get a firm quote as insurance may be crazy for an 18 year old. Mine is about $80 a month full coverage.
I have only leased one car in the past. I see benefits in both leasing and buying and I know you MAY have tax benefits with leasing with you owning a company but I found the Hellcat lease was not a wise choice for me as I may want to keep the car long term and the lease residual just did not work on any Challenger. However, my dealer was fine doing a Hellcat lease for me. I do know a lease is for better credit.
People will disagree with me but the numbers did not work and the monthly payment was not that much lower than a purchase with 10% to 15% down. The interest rates on a purchase is great right now with good credit. IMO almost free money and for long term as well. FYI, in July 2015 with good credit I was quoted 2.29% x 75 months from the dealer and my credit union was 1.99% x 75 months or 2.49% for 84 month with 10% min down. Use an online payment calculator and amortization schedule to figure your payments. IMO as a minimum with 10% down you are looking at $750 to $850 a month for financing. A lease may be a few hundred lower. The Dodge site will estimate a lease payment for you.
My suggestion is do your homework and even if you get dealer financing know what your options are upfront when you walk in.
Some folks are paying high $$ over MSRP. I say find a dealer that does not charge over MSRP or say under $1,000 over MSRP. I found one but you gotta look.
just my $002 and trust me I can tell you everything not to do at 18 as I made all the mistakes but had fun making them!