You can put the extra cash in a visible place next to say your car keys or glasses and mobile phone, then say to her as you jump on the table, "By the way, today I have spare cash for a special treat by you if you want to do it."
She then looks at the cash and will know it's hers if she gives you more. Usually, the girl will ask back "What do you want?"
You can then make your offer..... for example, "I have 150 if you're ready for sex."