Sites like FareCompare.com allow you to compare several sites at once, which is handy. I also sign up for airfare alerts for local airports; sometimes there are super good deals.
Additionally, it’s best to book midweek, like Tues-Thur, as fares tend to be cheaper those days. It helps to also pay attention to the time of year. Right now should be a good time, as should Sept. or Oct., basically the times when less people are traveling (higher fares during holidays and summer).
I’ve flown to Italy roundtrip for as little as $450, and as much as $1300. Fares vary a lot depending on many, many factors. You just have to be patient and vigilant and you should be able to find something more affordable. In my experience, the sooner you book the trip prior to your desire departure date, the better. The fares tend to go up on a daily basis as they approach your departure date.
As a final resort, if fares just seem expensive no matter what, check out flying into X airport and then taking a budget flight via RyanAir or EasyJet to your final destination. Like, perhaps you might find a great deal for flying into London. You could take a cheapo flight from London to Germany via one of those two budget airlines (usually cheaper than taking the train in Europe).