I already have a buyer, what would it cost in commission to have a real estate agent take care of the sale from this point. This is in the midwest?

If you already have a buyer, why would you need an agent? It would probably be easier (and less expensive) to find a real estate attorney to draw up the contract and help you with any paperwork and the closing.

Agents can help guide both the buyer and seller through the transaction. There's a multitude of things that can go wrong and problems that can be missed during the title transfer, closing, obtaining the loan, inspection process, etc.

The agent is there to make sure things go smoothly and keep the closing on track. When you say "I have a buyer", does it mean they're fully qualified for a loan and know exactly what to do next? What happens if there is a disagreement or point of contention? Do you have someone who can help both parties understand all of the available options? Do you have a list of contractors, inspectors, handymen, title companies, and other related professionals that you can trust?

If he doesn't want to use an agent, he should at least have a lawyer look over overthing. I'd recommend using an agent because some may be willing to take less commission if you bring the buyer.

depends on the broker and agent as to how much commission they charge

Generally, the commission is negotiable, and most agents have their own price in mind for this type of service. I will typically ask for 2% to 4% to oversee this type of transaction depending on the price of the property and other factors.

You should be aware that a Real Estate Attorney WILL NOT preform all the functions that an Agent would. The Real Estate Attorney will only work most of the paperwork and title.... for about the same cost your agent can fully represent your interest and greatly improve the probability that you will close. The Real Estate Attorney would not assist you with any inspection coordinations, appointments or workout any problems. They will not provide any follow up to mortgage applications and approvals, coordinate appraisal schedules or review them, arrange and coordinate any repairs needed by the buyer to obtain the loan, 3rd party review of your closing documents for obvious and hidden errors, or assistance in any other related matters.

Most brokerages will preform these task at a fixed fee rather than a commission. With the Sellers Market my area has been in over the past two years, we have preformed several of these for sellers and buyers.

depends where you live, usually 2-3%

I guess you were selling this yourself and the buyer was buying without an agent? You should shop around and go with the real estate professional you feel you can depend on most.