Bethenny Frankel -- It's Expensive to Divorce Bethenny ... For Bethenny

Bethenny Frankel's divorce has dragged on so freakin' long that now she has to fork over $100k just to cover her soon-to-be-ex husband's legal fees -- even though they've yet to agree on terms for a divorce settlement.

According to court docs ... Frankel has to immediately hand over what amounts to an advance payment to Jason Hoppy's attorney. The docs stipulate the $100,000 will be subtracted from whatever financial settlement Jason ends up getting from Bethenny ... presuming they ever hammer out a deal.

Frankel filed divorce docs in Jan. 2013 ... and they've been battling over money and custody issues ever since.

Frankel sold the Skinnygirl brand for about $100 mil, so technically 100K is a drop in the bucket -- but since it's going to her ex's lawyer ... we doubt there's a smiley face on the check.