Not sure if the foam route is a good option, it works in recording studios but it is going to accumulate sawdust(if machining wood) and this could be a fire risk.
on the boats i used to work on fiberglass was used and this was covered with perforate board, all openings need a good seal also and if your dust extraction equipment is outside i would think the noise would track through the system. you need to do a web search for acoustic insulation companies and get more info, it won't be a cheap operation.
Regards
Mike