Calendar - Picking your collective brains...

I'm looking for a calendar program that I can integrate into a website that I could put community events into, and even attachments. (Like a registration form for an event, or flyer or something like that)

At the same time, I'd also like to authorize a very limited number of people to add things to the public calendar as if they were me.

I'd like users to be able to just 'click on a date', or even do a search for events and have them pop up.

Not sure if it matters, but the website will be under it's own domain, and eventually on my own server. Not sure of the format yet, although we'll be using Wordpress for part of it.

I've played with Yahoo calendar and Google calendar, both of which could do some of what I want, but I find them to be awkward and subject to "not loading". I think I need something a bit more stable and professional.

Anybody have any ideas where to start?

Oh yeah.

The cheaper the better!

Thanks!