What the dealership wants to do, besides rope you into another contract or get your bank check up front (even better for them) is get a slightly used car and rip you off for it.
NEVER tell a dealer what you want to pay per month. There are 20 ways for them to make a payment for you total $XXX per month and all of them will rip you off.
Here's the scenario:
When you come in, they offer you some sexy new car for $19,000 and you get all wide eyed and they tell you how good it looks on you and how your manhood will grow and inch and you'll grow hair on your suddenly developing chest muscles because of this new car.
Then they knock your socks off by telling you that with your trade in you can have this brand new car for only $13,000, they don't even care if you use Mazda financing since they are such good guys. The loan you owe will go away too.
Shoot, you figure you paid more than 12 for your new P5 so you really got one over on them.
You say "Where do I sign?" and they run up the numbers for you and you are on your way after an additional $500 delivery charge and tax/tag/title and undercarriage rustproof for $500 and maybe a filing fee of $50 or so.
You roll off the lot laughing to yourself about how you really made out on that one... Plus they gave you a free Mazda keychain wich will impress your buddies.
They walk back to their office laughing too, because here's the deal:
They just got you to turn in your car to them for $6,000, they'll hose it off and sell it for a "no haggle" price of $10,500. That also happens to be PURE PROFIT for them.
They moved a new, or earlier model off their lot, which bumps their quotas with corporate.
They also got you to either:
1. pay with your own bank and they get all the money up front which looks good on their books
2. pay with Mazda finance which is good for them in the long run because of the interest you'll be paying right back to Mazda corporate.
Since you let it slip that you want $400 each month payments they made that happen and after all is said and done you'll pay $26000 for that $13,000 loan due to interest.
Do the math, they got you to pay $26,000 with financing, and $4500 extra for the trade, plus about $500 in random bogus charges like delivery and paperwork, plus maybe $300 in fluff "extras" charges like floomats and locking lugnuts or exhaust bearings (I've seen window stickers with a list of extras that were not even installed on the car).
SO: $40,300 sound good to you? (yupnope)