things are constantly changing so there's no avoiding trawling through the booking sites to find a good deal
Well, there is an alternative. Its called ITA Matrix.
To quote myself from a previous thread on the topic ...
There is a learning curve, so prepare yourself to do a lot of reading, and a lot of testing but as free tools go, you won't find anything better.
Sure you can't book on ITA. But if you want to find the best deals, you'll seriously struggle to find a better tool.