$18 grand in 1969 was ALOT of money! Creedence were paid $10K for Woodstock 1969, The Band, Janis & The Jefferson Airplane all made $7500.
Here's the full payout list of Woodstock performers & how much they got:
https://consequenceofsound.net/2015/03/heres-how-much-each-artist-earned-from-playing-woodstock/