What's a good price to pay for a students sketched drawing(portrait)?

I agree with Stephen: Go to a college instead of a high school. And, I would look online at the college's website and find the Director/Dean of the Art Department. Ask him/her if he/she could put you in touch with a drawing instructor or a student who could do it. You might want to ask the teacher/student for examples of their work, too.

Another option is to search a website like DeviantArt.com or Flickr. (I think eBay has a Services section on their site. You might check there, too.) A lot of artists post work on the first two websites I mentioned. Find a good artist whose sketching work you like. DeviantArt allows you to filter to a specific type of artwork. A lot of these artists also have websites where they advertise and offer their artistic services. (You probably want to use one that has PayPal for your own protection.)

Another option is to use an image software program. I use Paint.Net (free download at CNET.com) and it has a filter that can make a file look like a sketch. It won't cost you anything except some time to try this method.

First of all don't go to a high school, go to a college.

Second of all, artist are always looking for practice of drawing the human figure so I'm sure you can get it for free if you model. But if the artist has an ego throw him $5-$20 based on YOUR income.

A six pack. Where were you when I was a student.

well for a3 pics done of you in new york, you can get one done for about $20. i would suggest that same amount.