Sexyy Red's flashing cash and flaunting her new look ... 'cause she's proving she's got money to burn in her new post showing off her $30K boob job.

The rapper posted to her Instagram Story today ... sharing a series of videos from right after she got her breast augmentation -- rapping along to a few songs on the radio while bouncing her chest around.

In one pic, Sexyy confirms exactly how much she spent on her new ta-tas ... saying she threw down $30K -- so, she didn't cheap out on this plastic surgery.

But, don't worry ... SR's clearly got a whole lot more to spend -- 'cause one clip shows her holding a huge stack of cash, stunting on her fans with her hundreds.

We told you yesterday that Sexyy Red planned to undergo her third breast surgery to redistribute the weight of her breasts ... all in an effort to fix back pain and improve the fit of her clothing.

It looks like Sexyy's quite happy with the results ... and, we know she'll have ample time to recuperate -- 'cause her makeup line Northside Princess is taking off, and she's happy to rake in the dough while putting music on the backburner

Given how happy Sexyy Red is in the clip, it's clear this surgery was worth every dang penny!