What is keep it a buck fifty?

Willing to bet how ever much money you say, that the statement you make is true.

Let me keep it a buck fifty, pizza is only meh

Or

Imma keep it £3.68 dogs are better than cats

keep it a buck fifty - video

keep it real (as in candid or blunt). usually said when giving a harsh truth to someone.

“Imma keep it a buck fifty with you, this song sucks”