Loading the main is just as much an issue as cost of wire. Go price the cost of upgrading a main service.
EDIT. For those that don't understand what I mean by "loading the main" , electrical inspectors start by alloting so many amps /sqft for lighting and wall plugs. Then they add in all your 220 volt services such as water heater, clothes dryer, range, pool, central AC etc. Depending on the size of your main service, you can easily reach your allowable max. A 50 amp service is probably more than central AC, pool, and water heater combined. When you reach the max, the only solution is a new main panel. $$$$$$