David Geffen's Estranged Husband Says $50K Per Month Isn't Enough

David Geffen's estranged husband says the mogul's trying to cheap out on spousal support ... alleging David's only offering a fraction of what he spent in a month while they were married.

David Armstrong -- also known as Donovan Michaels -- filed documents Thursday in which he claims Geffen's trying to "aggressively limit" Armstrong's access to temporary and permanent spousal support.

Armstrong objects to Geffen's request that he only pay spousal support for a few more months. He points out David's worth a whole lot of dough -- $8.9 billion according to Forbes -- and Armstrong says he has firsthand knowledge that Geffen still works as a "venture capitalist, high-level investor, and power broker" despite Geffen's claims that he's now retired.

It all comes down to dollars -- and a whole lot of them -- Armstrong adds ... 'cause $50,000 a month isn't nearly enough. Especially since Armstrong says Geffen spent more than $3 million every month on living expenses while they were together ... and Armstrong believes he has a right to keep living that same lifestyle ... which he can't do on the 50 grand Geffen's offering.

Also, Armstrong's team alludes to some alleged harm Geffen caused him ... writing in legal docs that Geffen "solicited Donovan when he was a vulnerable young foster care graduate and thereafter perpetrated physical, emotional, and psychological harm on him."

In Geffen's reply, his legal team -- led by disso queen Laura Wasser -- argues he's already paid Armstrong $400K since they separated ... and he's allowing Armstrong access to his $15K-a-month New York City apartment, rent-free. Geffen also says he's working hard to settle this divorce ... while accusing Armstrong of seeking to delay a resolution of their split.

Geffen filed for divorce in August after less than two years of marriage ... a shocking split given the two men didn't enter into a prenuptial agreement.