You could ask them to show you how they got to your $584 monthly.
The monthly payment is composed of 3 main parts
(1) Depreciation: this is the amount between the selling price and the residual divided by 36 (months). So your residual is $51,200 * 0.62 = $31,744. Based on your info, it seems like the sell price is $51,200 - $2000 - $500 - $1000 = $47,700 … ~$443/mo
(2) Interest: With the MF of 0.00038, that is < 1% interest so a couple of bucks a month
(3) Tax: 9-10% (WA?) * your monthly so maybe $40/mo
If you can figure out what is going on with each part broken down, it will be easy to see where you can get to $440. It seems like the best place for you is to figure out the actual discounts you are getting from MSRP - how much are they going to sell the car to you for? That will drive down (1) Depreciation … everything else is already good specially with the MF with your MSDs
How should i negotiate the price of the car since its so new? KBB doesnt even give me a number. Truecar give me a market average of $48,916 which seems high
Absolute numbers are less relevant than % (off MSRP before incentives)
You should be aiming for below average (by definition, half the people paid below avg). Where you end up depends on how competitive your local market is.