There's a site called blogtalkradio.com that let's you host your own show for a specific amount of time with a call in number for your guests and a chat room people can join. You can turn these features on & off or just do one or the other. You can set it up any way you want take a certain amount of callers, limit questions to 1-2 per caller, answer emails live on the air etc. The shows would even be available for those who may have missed the live show.
I'm not sure what the charge is, however I know a few people who do it & it seems to work out great.