Probably the most expensive tickets I bought were $150/each tickets to see Billy Joel and Elton John in concert together. Awesome concert!
Other than that, the tickets usually top out at around $100. Often less than that but the price become "notable" in my mind if exceeds $100. That wouldn't rule them out, but it has to be for something really good. Just recently got front row seats for Cirque du Soliel for just about $100, totally worth it!