There is a reason I sold my 08 Cooper S...
Look into:
Death Rattle aka. Timing chain rattle, tensioner failure
Fuel Pump Failure
Cold start issue
Loss of Power Steering
Loss of electric fan
Carbon build up on exhaust valves
CVT transmission failure
If you are making the money you say your making, you will not be able to afford the Cooper S.

 

I say buy a cheap bike also. 8's are too nice! If you really want to get rid of the 8 though, I'd say get an MX-5 or used S2K...

 

Another chime in on Mini S MPG:

I had a 2011 MCS, and when I drove it any more aggressively than an octogenarian, I received 19-21 mpg in the city. I am driving my RX8 much harder and getting 15. If you are a spirited driver, the MPG might not be the deal breaker you think it is.

I have heard the MX5 is far better on gas and the wallet...

Zelig

 

My wife gets 22.5 mpg in her Mini S so don't expect too much.

 

Doubt you'll get anywhere near 16k for the car unless its very low mileage or if the dealer gives you the discount on the mini as part of your "trade in value" acv(actual cash value)+discount and presto! we can give you 16k for your car!! The Mini is an excellent choice by the way.
My 2009 MX-5 averaged 27mpg and was nearly as quick as the Cooper-S without the worry of turbo reliability. MX-5 0-60= 6.7 seconds which is also nearly as quick as an RX-8 incidentally.

 

Massively loaded request.

Right off the top of my head, I would say a Fiat 500.

It unique.
It gets good gas mileage.
And I would recommend one to a 17 year old boy, just starting out driving, because they have the crash protection of a small tank. Several different reports of SUV's being totaled by hitting Fiat 500's on a couple of the different forums out there.

BC.

 

It's funny, at 16k, you're approaching Lotus Elise territory.

 

Then your Cooper S could burn to the ground:

http://content.usatoday.com/communit...tion-recall-/1

Buy a new car when you can't afford gas money for a free one? Sounds pretty silly, aka dumb. The smartest choice you can make now is one that lets you live within your means and without collecting debt.

 

Not worth it buddy. Depending on the state, just paying the taxes on buying a mini would be equivalent to extra gas you would use driving the 8 another year. Plus you know your 8's condition pretty well i imagine. You never know what little maintenance things are going to pop up when you buy a new used car.

 

my wife just got a mini and it is a awesome and the MPG is amazing on it.... We push 32mpg in it or at least my wife does.

 

16k NOT a chance.....

dealer will give 8 to 9k (least the place I work does) tops

Probably less depending on the miles.

 

What about the 08-09 cobalt SS. It was the fastest FWD around the Nurburgring when it came out(probably still is at its price point). it gets 22/30 mpg. When car and driver tested it in their Lightning Lap not only did it have the fastest lap times among cars in its price point... but it even beat more expensive cars like the EVO X. Plus the eco tech engine is really receptive to mods down the line if thats what you're into. Plus you can get the four door version and have the ultimate sleeper.
Link to Car and Driver article: http://www.caranddriver.com/features...balt_ss_page_2

 

Just a thought, but if you buy a different car for the money you get for your RX-8 that gets twice the gas mileage (best case scenario), then you'd be spending $25/wk on gas. You'd save about $1300/yr on gas. If your money is that tight, then you'd be better off looking for a car that costs half as much as you'd get for your car so you'd have money to fix it when it breaks, needs an oil change, needs new tires, etc. Can you car pool, ride a bike, take a bus for less money, etc half the time? If so, then just keep your car and you'll be better off financially. Otherwise, you'll probably regret it for a long time.