Tools, tools, and more tools. Deciding on an arcade monitor vs a tv, etc. I figure the tools to be a good cost being if you by a prebuilt cabinet from mameroom.com you will spend $500 easy. All the tools and MDF was about that, so I guess it's not all that bad.
Don't misunderstand, I not really gripping about the cost since this is a project that I didn't need, but it something I wanted. And wanting something bad enough the costs is less of a factor than the return.
Saying the part about unexpected costs will hopefully shed some light to those starting just as I am.