Well you've got a few options for ham antenna mounts and it all depends on the antenna you plan on using which depends on what bands youll be using. To keep it low cost and simple (well relatively), i would just get a 2m radio. So for the antenna, i would recommend finding one that is a 1/2 wave if its going to be mounted on the rear bumper as 1/2 wave doesnt need a ground plane to work well. After you figure out what antenna you want, then you'll know which mounting option you need.
As for mounting options, There is the 3/8" stud that is the same as what is standard for cb antennas, then you have the popular nmo mount, then you have the pl-259 mount.
Most nmo mounts require a 3/4" hole but some require only a 3/8" hole, while others require a larger 13/16" hole. I'm not sure the size hole for the pl-259 mount but I'm sure it would depend on the mount used, as it varies.
Cliff notes: jumping into ham requires alot of reading and research, unlike cb, its requires a little more knowledge but thats what separates us from the little kids on cb ;-)
I would have hefty weld on a tab that will accept at least a 1" hole but i wouldnt have him drill it. When you figure out what route your going to take, you can drill your own hole to fit the mount you choose, rather than having to go through the headache of having a hole that's too large or too small.
