They land it... kinda the point?
1'x1' squares of foam = $1.00 each. Kenny's pit = 100,000 1x1 squares. $100K just for the foam. Then something to hold it all together, a moveable roof to keep the foam dry, a ramp or two, some land for run-up, something to get you and the bike out of said pit = $200K - $300K.
Good luck with that. Of course a BMX pit would require less, but ...
From his (Bartram's) pit in 2005 (DirtWeek) The infamous, BigLou:
Used a bobcat with this boom to pull riders out.
Name the guy on the bike and DRN'ers in that shot and win a "prize".