Ando goes as low as $99 per station to license AdInjector, but I don't know if that will guarantee you ads. We'd be willing to pay that per station to get some spots. People operating on the free version of basic stats monitoring get nothing but the lower-paying bulk-buy AdWire spots.
Working with an ad agency compatible with Ando, such as TargetSpot can help you get some ads on your station based on your audience. Not sure if they're still interested in mom and pop online radio stations (especially after signing radio giants such as CBS for their ad services) but it's worth a shot!