Are you sure you want 4' x 8'
Are you sure you want 4' x 8' sized map, that really hugh! I digitally print maps at my print studio, Gamer Printshop, but even my printer is limited to 42" wide, so I can do a 42" x 96". Still that's gargantuan. That $83.72 for just the print. Unfortunately I can only laminate 36" wide, so I couldn't do one the size you're looking for.
While its true I've created maps this large before for a client, I've only done it once. That's crazy big. DPI wise, you would only 200 ppi, depending on how small your text size is, that's where resolution matters the most.