the main differences are not the finish, it's mainly the type of wood used for the fittings. the cheaper ones use cherry wood(formerly rosewood or maple), the more expensive one use ebony.
Ebony is a much harder, longer wearing, and much more expensive wood.
Difference in sound is not that great (within body shape) in my opinion, a ES9 and ES1, don't sound that much different than the EM1. whereas the EG9 and EC1 sound similar.
But string type and setup make MUCH more of a difference than body shape.
You already have 3 recommendations on who you should buy from
Jerry Fretwell sets up his basses before sale, and that's a BIG deal. You probably could save $100 or so buying from somewhere else, but you have to spend WAY more than $100 on setup and strings on that bass.
I could have bought my bass for wholesale, but I bought it from Jerry Fretwell. His service is worth it.
Johnny