There are no typical amounts. The agent can request an amount which you can agree to or negotiate. Who pays is between you, the agent and the buyer. Generally, I like to get this issue resolved up front as soon as possible. The commission can be paid by either or both parties and who finds the home first really isn't a factor.
Here are some options. You can pay the agreed commission and just consider it a discount. You can increase your price by the agreed upon commission amount in order to pay it. The buyer can pay all or a portion and you pay a portion. Where an agent is involved, take advantage of their knowledge, resources and experience and realize there are lots of sellers out there hoping for a buyer. Be glad you have one.