When you buy a car in the higher tiers (3, 4etc), they will cost heaps as you know. So when you want to try something out and scared that it will suck, buy it anyway. If you do buy it and it does suck, then you can always sell it back for the same amount. For example, I bought a Chevrolet Corvette for about 220K, and upgraded it to the max. I tried to sell it and was offered $822,000!
Easy Money Grubbing
On any tier, but especially in tier two and above you can go to the quick race menu and enter in any of the races against "0" competitors and win the cash every time. No matter how bad or good you race. For example: every upper tier 'race' you win for tier 3, you recieve 20k. It's a good way to hone your skills and get the car you want as well as the money to max it out and get the works packages.
After loading up Career Mode, go into the quick race option. Then, select 1 lap, 0 opponents and the race track called 'Myatomi. ' It should be about 0. 38 miles long and it is a simple oval. Do the race with a tier 2 or above car. You can take your time as you have no competitors. When you finish, it will say that you came first even though you were racing against no-one. You will get $8,000!
If you want to level really really fast get a t2-t4 car and go on one of the small circle tracks put your damage to visual and select 15 opponents with 20 laps. You will get 6-10 thousand point per race and I'm level 32 and it takes me 3 races to level and its taken no time so good luck.
Quick Driver Points
In menu, go to quick race and choose 20 laps and 15 opponents. Then choose the track Myatomi. Then choose the Nissan GTR, with the WORKS upgrade. You will get 20000 cash, for winning, and you will get from 8000 to 16000 driver points. (Other cars can be used to, but the GTR is very powerful, and you will get many Spin Opponent, and Take Out Opponent points. ) I used 2 hours to get from Driver level 13 to 40!