Please don't let them decide on the price. You should cost everything out including time and then decide if you want to proceed. You need everything decided in yourself before making the committment. Many will support this and I don't care if it is a frend. You should not give a break until you know all the details. Then tell them and let them decide if they want to proceed. Initially friendship should not enter into it until you know what the full job and cost will be then decide if you want to give a break. Friendships can be hurt over such. You have to also know exactly what they expect as well. I did this one time (never again) and the friends expectations were different than my reality.