[M. Thatcher]

people who are willing to spend $3000-6000 to serve as a delegate

Campaigns can make it "worth their while." Perfectly legal.

[Vigilanteman]

And some do, for the right type of delegate. They also include a stipulation that you must reimburse the campaign for the value of the sponsorship if you vote any other way than pledged until such time, if any, that you are released. I’ve actually seen these type of agreements at the county and state convention level.