Best bang for $50

I have a medium keyword doing well.

"Cheap KEYWORDS" number 5
"KEYWORDS" number 15

What is the best way to boost the KWs for a budget of $50. Money site, long term.

Any ideas? Ninja SEO types. If anyone says "on page oppt ... "... Grrrrrr

You want to Hire People or
You just want ideas ?

Clear as a CRYSTAL