Overheard on Flashcoders:

Branden: [...] Also there is a *very large* ISP that will soon be rolling out a number of very affordable hosting plans that will include the FlashCom server. [...]

Mike Chambers: watch this url for information

So it looks like MediaTemple might come up with some offer including the new Flash MX Communications Server. This might be a nice way to get around that $4500´...

[UPDATE]

I should have read Mike's "Logged In" Column before...

There he writes:

Hosting
Macromedia has also worked closely with mediatemple, an online hosting provider, to provide hosting for Flash Communication Server applications. This means that you will be able to develop your Flash Communication Server applications using the Personal Edition and then host them from mediatemple’s servers.

Check out mediatemple’s site for more information on hosting and pricing. They should have information available within the next week.