When you search the city pairs and dates for your trip Google will tell you where prices rank currently compared to over the last two months. Right between the "Best Departing Flights" and "Other Departing Flights" is a box that says whether prices are high, low or typical, click on that and you can see the historical data. Be aware it does not include Southwest and only looks at the lowest price, on a ULCC if there is one that serves that city pair. I just looked at my trip from MKE-MCO leaving the 25th and it lists Spirit, which I won't fly, at $96 the next cheapest is on United at $323.