If Hollywood was Wall St. ... Ronda Rousey is Netflix -- 'cause her stock has EXPLODED this year ... so says Sylvester Stallone who tells us her movie rate is WAYYYY UP in 2015.

Stallone has worked with Rousey before -- back in 2013, he booked her for a role in "The Expendables 3."

But that was before she dominated Miesha Tate, Sara McMann, Alexis Davis, Cat Zingano and Bethe Correia ... making her one of the biggest stars in Hollywood!

So, when we asked Stallone if he was down to put her one of his next flicks, Stallone kept it real -- telling us he's on a budget and Rousey is simply out of his league.