I've pieced all the clues together and I've finally figured out what Mark is about to buy for his new ride....
It's a Pronghorn Antelope!
It's so obvious once you think about it. I was thinking maybe he was finally giving into his mini cooper temptation since he finally wants something with sweet gas mileage but that is to obvious. Then I thought maybe he's going to get a badass muscle car and completely surprise all of us but come on. Perhaps he is going to buy a really bad ass Jeep but then I remembered Jeeps make him cry. So, that leaves just the second fastest land mammal, the Pronghorn Antelope!
...You thought you could outsmart me Mark but I know your ways!