assuming this is
NON-turbonot tough, but not easy either
here are the actual instructions from my electronic Mitsubishi service manual...
Drain cooling system.
Remove necessary coolant hoses.
Remove timing belt.
Remove water pump mounting bolts.
Note bolt length and location.
Remove water pump
To install, reverse removal procedure.
Use NEW gasket and "O" ring.
Install "O" ring on coolant pipe, and apply water or engine coolant to "O" ring.
DO NOT apply grease or oil to "O" ring.
Ensure bolts are installed in original location
as for price...
if you do it yourself a good part from a good store will cost $50-$100, about $150 from the dealer and you can expect to spent about 5-6+ hours doing it yourself
if you pay someone to do the work you'll spend $500+
Sean