Have you asked fellow Texan marathon race directors for advice or just had someone compile a list of the prize purses for the top ten richest marathons in Texas?
I don't see much happening for your $5,000 payout.
You'll get a third tier Kenyan man jogging 2:25 and an Ethiopian woman who can run 2:38 to 2:42 depending if she has any company beside the escort bicycle. Promotion-wise it will be a failure because neither will make compelling interview subjects pre- or post-marathon. Local print and TV reporters will have trouble translating their answers...
"I feel very good", "I try to run fast". No, not a xenophobe, I've just seen it in dozens and dozens of races.
Doubtful an American post-collegiate will want to run for less than $100.00 a mile and if they thought they might go sub 2:20 or sub 2:40 and find 2 or 3 international runners with them or ahead of them at half will simply drop out.
There is easier money running two 10k's in a month and earning $1,000.00 to $1,200.00 by running 30 or 31 minutes for men or 34 or 35 for women. The marathon wipes you out and they wouldn't be able to race again for another month.
The comp entry is a given, they will arrive Friday night and leave Sunday afternoon and most likely will lay low and not attend your pasta meal less than 12 hours before the race.
Try to find more local sponsors because your 5 to 6 thousand prize purse won't really attract those runners that you think you want to attract.