Mark,
I have no idea how much you would need, could you not put soul nights on to promote your radio station, all proceeds going to your station. I'm sure you know enough dj's that would dj for you for free, or you could always find keen lesser known dj's to help you out.
a bit like a Solar radio northern soul roadshow as i say i don't know how much you would need but various venues around the country.. maybe have a word with established do's you could promote them on the radio and they could promote/support you.. if you get my drift..
I'm not always good at explaining things but i'm sure you can see where i'm heading with this..
Good Luck..
Mischief