You can get crossings pretty cheaply if you go through a travel agent in the States. When we went to book the tickets through Cunard, the prices from the UK were the same in pounds as the prices in the US were in dollars. At the time, the pound was much stronger, so it was a huge difference. I ended up purchasing them directly from the States, but if I had it to do over again, I'd try an American travel agent first.
We did the crossing because it was actually not that more than flying and paying for a bigger shipping crate for our stuff. We were able to take a lot of my stuff with us in our stateroom. Plus, we had only gone on one holiday since we were married, so the trip was worth it, even when you throw in the few days we spent in NYC.
If I had a lot of time, I'd do one of those freight cruises. They sound so wild. You just don't know when you will end up where you're going or how close you'll actually be.