It comes from the money that is withheld from each betting pool before the payout is calculated. This is known as the takeout. A percentage of this takeout goes to provide money for the purses. The percentage that goes to the purses varies depending on type of bet,(WPS, exacta, pick six) and where the bet is placed (ontrack live race, simulcasting site, OTW, phone acct). The 23 million is the estimate of what will be generated through these means.