I had Joe Locke's Rev-elation cd at the #1 spot on JazzWeek for eight straight weeks a couple of years ago and to tell you the truth, it didn't help cd sales much. It DID help with name recognition and some choice gigs. That can be achieved by sending promos to the best people (by reputation and "influence") and/ or the best stations in the country yourself. I mean, what does it really mean to have a station in say South Dakota play your cd 100 times? I would rather have it played in NYC, LA, the Bay Area etc. ( for the greater population and fans) and save the promo for a print review, or send it to a promoter. You can be very effective by sending out 100 promos in the USA. I put as much, and sometimes more, effort in getting releases played overseas. They pay a decent royalty, and frankly, that's where the audience is.
I would never pay for radio promotion. It's just not cost effective.