Is the ballpark figure of $900 a reasonable and fair price to pay for replacement of a timing belt and water pump?
It depends where you live. I live in the Baltimore-Wasington area, and paid $800 to change the timing belt, water pump, coolant, and serpentine belt on a 6-cyl Honda. I had estimates for the same work at your price, though.
Yes, if it includes fresh coolant, and replacing the timing belt idlers and a replacement front crank seal.
Chilton labor time says 2.8hrs OEM and 4.0hrs regular for the water pump (which has to also include the timing belt)
So . . . Mitsubishi time is 2.8hrs, and independent shops charge 4hrs . . . that’s how I understand it.
So, 4 x hourly rate. More if tensioners, idlers, cam seals and crank seals are added.
Plus parts
Plus tax
Yeah, it sounds reasonable.