The Pro account should be $9 or $10. You should move to dedicated server hosting, or to perhaps Linode, and drastically reduce your cost basis and dramatically improve your value proposition. 250mb of storage is nothing for $19 / month. The numbers just seem out of whack. Shouldn't customers easily be able to store a huge number of podcasts, given how cheap storage is? Store and forget. You want their content on your servers, all of it. For $99 / month I better get a terabyte of storage these days.
Slash your costs to the ground. Boost your value proposition to the sky. Dramatically increase how many podcasts customers can store on your service. You want them to stream your brains out, and you want it all to happen with bandwidth rates around $0.01 or $0.02 / gb.
With scale, and lots of usage, expand what services you offer to customers. Storage & streaming are commodities, so treat them accordingly, and instead focus on building a customer base with modest margins on the core, with an eye on what you can do with all those customers over time.
By going with the easy AWS solution, you're pinning yourself into a very tight corner on costs.
Again, all just an opinion.
