Kevin Costner's Estranged Wife Fighting Him Over Child Support, Scoffs at $51K

Kevin Costner's estranged wife is fighting for more child support ... scoffing at the $51,940 monthly figure he's currently offering, saying it's not even close to enough dough.

According to new legal docs, obtained by TMZ, Christine Baumgartner calls Kevin's child support proposal "completely inappropriate" ... saying he apparently expects their kids to live well below his means when they're with their mother.

Christine claims Kevin spends $240,000 a month on himself and the kids when they're with him ... a huge contrast to the $51,940 he's expecting her to need to take care of the kids when they're with her.

Kevin's estranged wife says the almost $52K simply isn't enough to provide for the kiddos ... pointing out it's well below the $65,000 per month she says Kevin was getting for renting out a guest house at his $100 million beachfront compound, where the family lived together.

Christine says there's just no way she can give their kids the life they're accustomed to on $52k a month ... claiming it's not enough to find similar housing or keep up their lifestyle.

In the docs, Christine says at the current figure the kids would be in for a big step down once she moves out of Kevin's home ... she says the kids are used to living at the beach and in a gated neighborhood, two things she doubts she will find at $52K a month.

Christine says she needs the money for more than just rent ... rattling off a bunch of other expenses like utilities and TV bills.

Kevin's estranged wife says the kids are used to having a team of people hired to maintain the home and the property ... including assistants and helpers who handle schedules, grocery shopping, food prep, cleaning and cooking.

Remember ... Christine's requested $248k for child support, with Kevin's accountant saying some of her expenses include more than $100k for her own cosmetic procedures and boutique shopping.