I went in feb to find out charges, I don't remember Avari as the hall had limited capacity and they suggested putting up a marquee outside but i refused as they had an open pool next to the proposed location - I'm pretty convinced a kid could fall into it but they didn't care!
We went with the marriott (khi) who have waivered the cost of the hall based on us booking 3 days worth of events with them in July this year, they're just charging us for the cost of the food per person which has worked out to be almost Rs1000. Decoration etc is additional.
By the way good things you've started looking now as these halls get booked up VERY quickly by foreigners (including myself). We went in Feb to make arrangements. And while we were waiting at PC someone booked a date in December 2010! Now that's some planning!!
Anyway congratulations and best of luck finding a venue.