Upgrading your processor almost always goes hand in hand with upgrading your motherboard and possibly your RAM also. Many motherboards support a couple different processor types and speeds although changing just the processor might not always be cost effective based on a limited performance increase.
There is no posted cost estimates here for this type of upgrade due to the specifics involved with inspecting the older equipment prior to knowing if changing just a processor can be done.
You will need to schedule a free inspection or consultation on a possible processor upgrade.