Coates saw his side demolish Bolton 5-0 at Wembley on Sunday and they will return to the national stadium on May 14 to meet an expensively-assembled Manchester City team.
He told the Sentinel: "It is much more difficult to reach the final these days. For 100 years or so it was a more level playing field but that's all changed over the last 25 years because of the money.
"It was an amazing scoreline. Nobody would have predicted that. It's just fantastic. It was a great day and I thought every player was brilliant.
"It was an amazing performance from manager, players and supporters. What a magnificent day for everyone. We`ve waited 147 years and now we are going to an FA Cup final. I'm very proud - it's a great achievement."
Source: PA
Source: PA