Many people assume they need to go to the overpriced dealer service route to keep their warranty valid, but that is not true.
If you really enjoy getting reamed in the wallet, that's a good reason to go to the dealer.
Another is for warranty service which is free.
Denying warranty coverage for having maintenance performed at the provider of your choice, or by yourself, is illegal by statute.
All that is needed is to keep records of the service done, or if by yourself, of the parts and supplies you purchased.
If the stealership is saying it's $400 for the first service, as
noted, which is basically a look at the car and change the oil service, I can only imagine what they would charge for something substantial. That price could be a lie to get you to buy their inflated plan, or if an actual quoted cost, they are thieves and should be avoided.
At many dealers, the first service is free. Two words of advice in this situation - "Run Away".
If you don't want to, or are unable to do the simple things needed to maintain your car, then shop around for a good independent shop.
The difference between the cost of either route will be substantial in ordinary circumstances, but likely huge if dealing with the loan sharks the other poster noted.