Looking For A Streaming Host With Variable Slots

First off about myself: I'm your typical knows-enough-to-get-by web design CMS flash type guy. Nothing special no real training but if I need to run a control panel I probably can.

What I need: I'm moving an AM station(oldies) to online streaming and need a host for it. The variable here is the only reason I'm moving the station is because a radio show on it which runs 1 hour every weekday needs to expand our audience and all that good stuff. We'll be expanding the show as far as we can hopefully within the next year and on certain days we'd have more listeners due to having higher profile guests on.

However, since we have the stream 3 other shows on the radio station have offered to pay for the costs(we had to get a cable line run to the station in the first place)- presumably they would have a lower listener rate.

The question is what's the best solution here? We don't want to pay for a 2000 slot shoutcast service right off the bat, but we also need one who can rapidly expand our slots as needed, or possibly have one which just charges based on use. When we get up to high volume would it be smarter for us to just lease an unmetered dedicated server (high assumption of 1000 listeners(which is months off) for 3 hours a day running at 128k bit-rate the bandwidth really starts to add up) or a dedicated server that just charges based on usage. The latter may even be cheaper than using the high-priced-slot-based shoutcast stream servers.

I figure someone out there has already done the research can might know an answer to the problem. The key here is flexibility- no point paying $90-300/month for a dedicated server the first month if we're only getting 200 listeners on our show and 50 for the other shows but if we somehow experience a surge in listeners we don't want to be stuck at a low cap.