For $15 a sheet my distributor will saw Dibond, plex, or whatever into as many pieces as I want. Joe does a terrific job, hits the dimensions spot on, edges clean as a whistle, all sides perfect 90 degrees. But the guy who sometimes substitutes for Joe is another story entirely, he takes full advantage of the distributors +-1/4 inch policy and it's pretty clear he would rather be doing something else.
So you take your chances. But the basic rule for all distributor cutting is...don't make the print until you've got the substrate or glazing. I slip Joe some pretty decent tips throughout the year, investments like that are worth it and it's cheaper than having an employee or a table saw.
If you plan to hand-feed 44" prints on stiff substrates, try to get a laminator that's a little wider than that, maybe 50". It's tricky to feed sheets through a laminator perfectly straight, and the very edges of the rollers don't pinch as hard as the center parts.