this looks like a good summary;

1) pay out money to claim or private purchase a horse.
2) pay trainer from $45 to $75 per day per horse.
3) pay ferrier $125 per month for trim and shoes.
4) pay vet minimum of $75 to the sky's the limit (highest last year for us was $880) per horse per month.
5) pay transport to move from track to track $75 per horse per one way trip. Out of state can be as high as $1,000 if going 1000+ miles.
6) pay $25 for vitamin "jugs" once or twice a month per horse.(seperate from the vet bill)
7) pay trainer 10%(of our purse money) if horse wins-5% for 2nd thru 5th.
pay jockey 10% if horse wins-5% for 2nd or 3rd, and $65 for 4th to dead last.
9) pay ponyboy $20 to bring horse to the starting gate per race.
10) pay $200 per year for licenses, partnership registration and silks registration.
11) there are lots of other smaller incidental expenses - to numerous to put down.