underground water wells

I would greatly appreciate if you could give me a solution to my well problem as I am at my wits end. The water coming out of the underground water well is coming out rusty brown and the water pressure is reduced. We had the whole system replaced only 4 years ago with many repairs in between. We just had an estimate for yet another well and pump for $3,000, this one supposedly has plastic components that cant rust. Is this so? I feel very confused. can anyone give me some info on wells and pumps? thanks so much in advance