I spent about 2 and a half million to beat the last mission. I kept dying right after the prison part, so I just rushed right through the early area with the other Allied Tanks, just enter the prison and the enemies you left alive aren't a problem.
As for the parts after that, Air Superiority, Air Superiority, and Carpet bombing. I did arm a AA Launcher for a while to get rid of the choppers, but then I couldn't kill any tanks. So I just called Air Sup when I saw more choppers coming and Carpet Bombed every kind of "barrier" the NK have set up. You'll get to a bridge you have a jump, before that, jump in the first Sungri you see and just drive past everyone, they are clueless.
The actually base was rather difficult, because you have a time limit and no real way of getting through a bunch of fences. So I punched boxes until they were close to the wall, and used them to jump over the walls.