Labor should be about 3 hours, so $80x3= $240 for the timing belt.
Labor on the water pump should be about 30 minutes so add another $40 for $280
Labor on the cam seals maybe 15 minutes so it sounds about right.
Your best bet for parts would be
www.jnztuning.net on Friday ( you may want to call them so you can get part numbers ) they are having a sale for Black Friday so you will save a lot of money as they already sell OEM Mitsu parts at about 15-20% off and are tacking on about 5% more in savings.
OEM/JNZ
Timing belt $78/$61
Water pump$157/$122
There are the differences just to give you an idea and that is not on the Black Friday sale price, that is thier everyday price, drop another 5% off for Fridays price.
Just remember, you will need a new tensioner, pulley for the timing belt, balance shaft belt as well.
Tensioner is about $45
Pulley is about $20
Balance shaft belt, I have no idea on the cost.
When doing a timing belt job, the balance shaft belt and water pump should be replaced as you have to take off the timing belt to get to the water pump, its cheaper and easier to just do it at the same time.