JMO
I run a series in Ohio , and I make no money at all doing it , because my business sponsors the top 5 payout and I pay back to all that start the feature from the entry fee's . I ran a traveling series of 5 to 8 races per year , running 3 adult classes . 350# , 400# and a RWYB , and start only 14 karts in the features (16 if provisions were used ) I also had at times a consi race for non qualifiers , that paid to the last place , so as to add to a comment above , not all of us are out to line our pockets .
Now as to the original question . Karting events are mostly a family affair , and do not draw much outside spectators .
Gate fee - $10 to $15 per head , we will use $10 to make it easy and here is why gate fee's are useful
200 paid thru the gate = $2,000
50 kids under 6 free = 250 thru the gate
Insurance - $2.95 per head ( Example ) =$737.50 ( Still have to pay for those 50 freebies ) - = $1,262.50
Entry fee's
Rookie - 0 - Trophy for top 3 - 5 entries ( $15 cost of trophy's , example ) This is kartings future , so I would give them all something , in the hole $15
Jr1 red plate - $5 - 6 entries = $30 - Trophy only to top 3 ( Same as above , example ) Back to even money .
Jr2 green plate - $10 - 5- entries = $50 - Trophy to top 5 ( $35 COT , bit bigger trophy's ) =$15
Jr3 purple plate - $10 - 5 - entries = $50 - Same as above =$15
Jr3 blue plate - $20 - 10 entries = $200 - 80% payout $160 = $40
Lights - $20 - 10 entries = $200 = 80% payout $160 = $40
Mediums - same as above = $40
Heavy - same as above =$40
Super Heavy - same as above =$40
Open - same as above = $40
Total of 81 racers paying entry fee's , this is just an example , more or less racers is possible
$1,262.50 +$390 = $1,652.50 Looking like a good profit so far
These are just examples
Staff - 8 - $50 per =$400 , includes flagman , scorer , 2 corner workers , 1 to put karts on track , 1 scale person , 2 in concessions , more if you use an announcer and or 2 scorers or another on track worker .
On site Medical ( EMT , Squad , ect ) $250 , if your lucky , but I stress this as a must.
$1,652.50 - $400 - $250 =$1052.50 Profit , Looking good !
But wait , I still have expenses , electric , track prep , property tax , restock concessions , fix broken items , ect. ect .
Even with a large number of spectators , 161 to be exact , that are non racers . I will be lucky to break even . I see this as a good example as to why gate fee's are needed .