I'm in need of someone to make me an online calender system for my members.

The calendar needs to have various options depending on what has been entered that day.
Users need to be able to send invite requests to other members and then once these are accepted the details of the meeting must automatically update into both users' calendars. The calendar must also be able to match two different peoples calendars to find availability.

Don't think a ready made, off-the-shelf style calendar will be adequate - Needs to be customised so that it looks the way i want it to look.

how much would a developer charge to incorporate such a facility into my website (its basically a customised form of an online Microsoft Outlook Calendar with meeting requests)