Lucid, don't pay a dime more than you have to. I run into this exact situation with the local dealers in the area. We charge the customer a license fee ($100-$163 in IL) and also a $150 document fee to do the the legal paperwork. The doc fee is legitimate and is printed on every buyer's order. Anything more than that is just pure markup. A lot of dealers will call it a "prep" fee. I've seen it anywhere from $250-$500. It covers the dealer's cost of gas, floormats, and detailing the car, so the customer is really paying for that stuff. If it's not printed on the buyers order, don't pay it.
Stick by your word and don't back down. Trust me, that sales manager is probably scared shitless because he's got a custom built car on the way and he just pissed you off. Eventually, he'll swallow his pride and get rid of the fee.