Bose Acoustimass 15 Amplifier

I am looking for a good (and cheap) amplifier for my new system. Any suggestions?

The system (mine is in white) :https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwjyxcus6bPVAhUM9IMKHdh1DtUQFggtMAE&url=https%3A%2F%2Fwww.bose.com%2Fen_us%2Fsupport%2Fproducts%2F5_speaker_home_theater_support%2Fam15_series1.html&usg=AFQjCNF7wNFmcYmBwGiD71zO7DmiJvio_Q