Extremely low. When you're going up against democrats and Republicans, you're going up against their donors too.
But to be fair, sanders got far with individual donations and Trump won despite losing a lot of funders so who knows.
The tragedy is that this country's democracy is a facade. Beneath the facade is the real power[the Supreme Court and the electoral college]
If even by dome miracle someone like Jill stein or cornel west gets the popular vote as a write in or ballot candidate, the electors which comprise the electoral college will not have foreseen that result and they'd have voted for Trump or Biden. If there's a discrepancy between the popular vote and the electoral college, the EC votes decide the election.