XXX Honcho to Octomom Nadya Suleman -- Your Porn Stock Is Plummeting

Octomom's topless photo shoot didn't completely sabotage her porn future ... but it did drastically reduce her XXX market value -- this according to a brand new porn offer from Vivid Entertainment.

In case you didn't know, Vivid honcho Steve Hirsch offered Nadya Suleman $1 MILLION in 2009 to star in her own skin flick -- but Octo turned him down.

Hirsch made a second offer in 2010 to help bail her out of foreclosure -- $500,000 for ONE hardcore scene -- but Octo rejected that too.

Now, in the wake of Nadya's topless photo shoot, Hirsch is making one final push to lock the mother of 14 into a porn contract -- except this time ... he's not offering 7 figures ... OR half a million ... not even close.

Hirsch sent Octo a letter yesterday, offering her a paltry $100,000 to appear in THREE hardcore sex scenes -- claiming, "Regrettably your market value has diminished."

She might need the money, but don't count on Nadya chomping at the bit any time soon -- Octo called in to TMZ Live yesterday, and seemed pretty adamant she'd never do porn in a million billion years.