1993 GS300 need new amplifier

Hi, I have or better said had a Pioneer amplifier in my 1993 gs300 and now it doesn't work. I called the local dealer to find out that they are asking 494.00 for the amplifier. Does any one know where I can get one or is there a way that I can just get an after market one or better yet just change the radio and update it with a cd player etc. any help you have or suggestions please. thanks