no idea of costs, but it is usually much cheaper if you can remove the locks and take to them, rather than having them come to you. Depending on the brand and type of lock, it might be cheaper to simply replace the locks. there are also “DIY” re-keying kits on the market

That will probably depend largely upon whether you have the locksmith come to you or take the locks to the shop. Here, in the Northeastern US, it usually costs between $12 – $18 to have cylinders re-pinned at the shop, while most locksmiths will charge an additional 35 – $50 for a service call.