Its wide open. Did you pick what this truck is gonna be? Mt,racer,basher,on road, sand rail, etc...?
If I am buying a stock roller, I want to keep as many parts stock, to achieve the initial goal. If I am going hog wild on a build, I will skip the roller, and just buy hop ups, and exactly what parts I need. I built a hog wild bandit up from a roller, and in the end, not 1 part of the original roller was left = wasted money on roller.
If you have the exact vision of what its gonna be, get the most expensive stuff first, that way the end of the build is accelerated. I would expect the most expensive parts would be the electronics.