1995 Toyota Avalon Exhaust System

Hello,

My 1995 Toyota Avalon, according to my mechanic needs a front pipe and a rear oxygen sensor. There is some part of the front pipe that has come apart due to rusting and my mechanic says the entire pipe (system) has to be replaced. The cost estimate is at 1600.00 including labor. He says that for vehicles that are 96 and newer, you cannot use an After market part because that will cause the check engine light to come back on. But since I have a 95 model, it can probably be tried out as a cheaper option in my case. The oxygen sensor he say would cost about 200 bucks including labor ($80/hr). What are my options here? Does the whole pipe have to be replaced? Is the price quote valid? Any help would be appreciated.