I need help determining ad rates

The web site I own and operate http://hi-techreviews.com has finally become more active an now companies that have supplied me with products to review in the past now wish to purchase advertise space for their banner ads on my site.

I know that I can basically give them an option of 468 x 60 banner, 600 x 125 skyscrapers or any other 125 sized block, or one 768 footer banner. Now my question is this, my site is currently averaging about between 7,500 - 10,000 visitors a day depending on the day. (Yeah I know that's small potatoes to most sites but it's also a niche site.)

What would be a fair price per 1,000 impressions for a front page ad on a site like this? I don't want to price myself out of the game, yet I don't want to give the space away either and lock it into a 6-month contract when someone might offer more money for the same space.

I used the Overture Bid tool to see how popular these particular sponsors were and their were in the high 11,000 to low 12,000 range yet one was only at 900 so you can see I am running a mixing bag of potential advertisers.

If anyone can offer some advice it would be greatly appreciated since most of these companies are getting ready to set their new marketing plan in stone for the coming year and I would really like to be included in it.

Thanks
Kevin