Mike,
I have never looked at it from the cost standpoint. What is a must for me is that I can cut parts submerged that you cannot do, or do with great difficulty on a non submerged machine. I have a prototype shop for the most part and need to run everything that comes in the door. It kind of depends on what type of work you will be using the machine for. The thing to keep in mind is that you have superior flush and heat sink with a submerged machine so you should be able to hold closer tolerances. I cannot address the surface finish aspect as I don't have the experience of running much non-submerged work. There have been times when I have had to run in non-submerged mode because the parts would not fit in my work tank and I have had to build an outrigger 10' out from the machine to do one job. ( sharpening long carbide tipped boring tools for drill holes for rock blasting people.)
Personally, I would not invest in a non submerged machine.
TMD
