Frances Bean Cobain's Hubby Wants FAT Allowance

Frances Bean Cobain's estranged husband says he won't have a penny to his name without her ... so he's asking a judge to make her pay up.

Isaiah Silva is requesting spousal support, and according to the docs he wants a ton of it -- nothing less than $25k a month.

Isaiah says he left a steady job when they got married and Frances promised to cover a bunch of his monthly expenses, including paying private school and housing bills for his child from a previous relationship.

Now, he says Frances wants to renege on those commitments. Isaiah claims Frances has upwards of $100 mil in her dad's estate, and says he deserves half of the money she earned off business deals made during the 2 year marriage. He says there's no prenup.