Went thru this whole headache last spring when we built our place. First quote for an oversized stained wood entry unit came back around what a used car costs, and I nearly fell over. Took me weeks to figure out wether I was being robbed or if that was just the market now.
The size is what kills you. Once you go past a standard 36 by 80 slab, you're in custom territory, and the price climbs with every inch. Big doors with sidelites mean wider jambs, custom thresholds, beefier hinges, and way more shop labor. Wood species shifts the number a lot too, so it pays to compare a couple before locking in.
Two things that actualy helped me. Ask exactly what's included in each quote, prehung vs slab, finish, hardware, glass, delivery, because one quote might look cheap and be missing half of it. And get a bid from a local millwork shop, not just the big box stores or the online outfits. My local guy beat every other number and let me pick the species myself instead of pushing whatever they had in stock.
Also ask about lead time up front. Custom units can take months to show up, and nobody warns you about that til your house is sitting there with a hole where the door goes.