Kevin Costner's $129k/Mo. in Child Support Insufficient, Christine Wants $175k

Kevin Costner's getting off easy paying $129k per month in child support ... according to Christine Baumgartner who wants that number increased to ensure their kids keep living large when they're with her.

Christine filed docs, obtained by TMZ, asking the court to reconsider the amount of child support Kevin pays due to 2 factors -- 1. making sure the kids enjoy the same lifestyle with both parents, and 2. what she's learned about how much money Kevin's been making.

She lays it out in the docs, explaining their 4 children live in a beach compound with their dad that's worth between $65 million and $95 mil ... and they also fly private on luxury vacations with Kevin.

You'll recall, Kevin took the kids to Aspen last month -- right after Christine had them in Hawaii. She says Kevin needs to pay sufficient child support "so that the children can go on comparable vacations when they are with her. This is true even if the child support payments also improve Christine's lifestyle."

Christine says that's simply the standard required by California family code. Based on that alone, she says the $129k/month won't cut it, and she's instead estimating $175,057/month.

And by the way, Christine says that's a deal because that higher amount "will not be sufficient to replicate Kevin's lifestyle, but it will be sufficient to allow her to provide a lifestyle for the children which is relatively comparable."

Now, as for Kevin's income ... she says his average cash flow for the last 2 years was $19,248,467 each year, or more than $1.6 million each month. Based on them having 50/50 custody of the kids, she claims California guidelines require Kevin to pay that $175k/mo. she's requesting.

And, she paints a very green picture of Kevin's career ... claiming he made $11 million for Season 4 of "Yellowstone," and $10 mil for Season 5. Plus, she says he's scheduled to make $12 million for his upcoming "Horizon" film, and another $12 mil for the sequel which has already been greenlit.

By the way, Christine's been house hunting -- she says she's currently living in a vacation rental, but in September she's moving into a month-to-month rental in Montecito for $40k/month.