do a search on this website....this is answered about once a month.
Low oil pressure could be a result of a blocked pickup screen in the oil pan.
I would also be inclined to check your oil sender which tells the guage the pressure. I had to replace mine because it was faulty. It simply unscrews off. If it is clogged, it'll give you false readings.
It isnt hard to replace an oil pump...biggest pain is dealing with the pan. If it bothers you that much after the aforementioned items are checked, go ahead and replace the pump.
As to what is normal, it should read at least 30 lbs pressure when running, or 15 when idling--or somewhere close. Mine reads a constant 45 in my sub, and 60+ with my 383 stroker with high volume pump.