Question about vehicles

Ok so there is the huge open world. I have the 4x4 wheeler that u get with the opening quest. now my question is how can you get the others, examples the transport or the one with the mini gun. I don't see anywhere even on google where each vehicle is explain where you obtain them and at what cost or even where you can use them, someone please help me out on this.

There are some vendors around the map. I know there is one down south next to a mods vendor. Hope this helps.
:-)