how long would it take for a shop to change my oil pump, or should i change it!!

The 2.5L should take around three hours, the 3.0L would be more like five. It will take them longer simply because something like that usually takes longer than book time, and it isn't as though they can start working on it the minute that you park the car. I have no idea on parts cost or labor in your area, but I would imagine that the job could get quite pricey. If you aren't willing to spend $500-1000 on this car, then I might consider other alternatives. Also, why do you think you need an oil pump?