How many years racing experience do you have?
How many podium finishes under your belt?
Have roughly $250,000 USD/yr. For a bike and skeleton crew to run as a privateer in lower level racing (assuming you have a decade or so of track experience)... ?
You don't just walk into GP racing. You need skills and financial backing.
Most racers start competition as teens, if not before.
I recommend buying a used lower displacement track bike (assuming you are not already a seasoned racer (hence, the question)), then going to some track days.
For ~$20,000 USD (beat up bike, beat up truck to haul it, gear, and fees), you can to do some hot laps at a track a couple times a year.