Let's see......18 cup with a cup being 8 ounces. 18 x 8=154. So you are starting with 154 ounces of water. Divide that by 6. 154/6=25.6 rounded up to 26.If your brand of coffee calls for one...
This totally depends on which size of coffee you decide to purchase.
You can get a cup of coffee for as little as $1.50 and as much as $5 at high-end coffeeshops.
I drink espresso and it went up by about 40 cents, it might be the same with regular coffee. (BTW that's Starbucks prices dunno about other places)