Three letters, Lightspeed: R, S, C. Three words after it: Rally Raid Car. One company: Toyota. You can get it easily by winning the Capri Rally (Easy) races. What is Capri? In this case, it isn't those mid-length pants girls wear, it is the beautiful Costa di Amalfi course. Here's one important hint for you, Lightspeed, you don't need a rally car to win a race on tarmac. You want varification of this? You face Le Mans race cars with Tsukuba Circuit WET in the Hard races. So then, it leaves you wondering what you have to use.
For the tarmac rallies, I tuned a Mitsubishi 3000GT MR from... I want to say 1998. It is already a powerful machine, with a few more mods, you can't lose. In fact, the only real trouble you're going to have on tarmac rallies is Citta di Aria. Anyhow, after you win the Easy version of Costa di Amalfi, you get the Toyota RSC Rally Raid Car. Unlike past GTs, you have to purchase off-road tires seperately. Having Dirt and Snow tires are important for even entering the off-road races. Both will cost you about 22,500 Cr for each one. So you're looking at around 50K credits to spend just on Dirt and Snow tires. The RSC Rally Raid Car has been the only rally car I've used except for when I won myself a Suzuki Escudo Rally Car. The RSC is very powerful, yet very controllable. As long as you can race as hard as you can and eventually win, you're almost unstoppable in this machine.
Now go win you some rally races. Oh, and if you need money from them, most of the rally cars go for about 100K to 200K. Unless you're going to use all of your prize rally cars, you can easily make some money.