I'll give you two answers here. First what is fair and second what is a great deal.
A fair, good deal is $500 to $1,000 over invoice. The dealer makes some bucks, you get a deep discount (around 4K-ish) everyone is happy.
Many people here, especially those who purchased from late October to year end got below invoice deals (I got at invoice). Because popularity of the Avalanche is increasing and the economy is picking up, those deals are going to be a bit harder to find.
The next issue - getting what you want. My strong recommendation is go to http://www.gmbuypower.com
Build the Avalanche you want online and then have it find them in your local area. Unless you want something like cloth bench seats with a neutral interior, you'll find one on a lot. Print it out and keep it with you. Go to a dealer and pick out any old Avalanche. Drive around, love it, seem interested, and then when you go back to talk deal you can say, "you know, I really like that one but it just isn't equipped the way I'd like. If I'm going to be spending 30K on a vehicle I want to get what I want."
Watch 'em dance then! Tell them what you want, they'll do a vehicle search and either a) lie to you about availability when you then walk or b) tell you that so and so has exactly what you want and they could do a dealer swap (but you already knew that part).
I also suggest you go to Edmunds, build exactly what you want and note what the invoice price is. Please note that the Edmunds calculator is kind of messed up, there is no conveinience [sic] package WITH a sunroof as an option so you have to check off conveinence package and sunroof as separate items.