We used Zara tours.

We did the 7 day Machame Mweka route in 2009.

It was possible to pay anywhere from $1300 to $5000 for this.

We paid about $1600. 7 day climb plus a day in their hotel Springlands before and after the climb. Highly recommended.

If you deal with a US based firm, they pocket half your fee and send the rest to the Tanzania local firm they partner with.

During the climb, we encountered other groups who had paid $3K to $5K to big name firms with US offices in NYC and SFO (and therefore lots of overheads). Their meals and tents were somewhat fancier than ours, but not 2x to 3x better.