I'm flying SFO to LHR, spending 3 nights there, then LHR to BCN, cruise, then 3 nights in BCN before flying home BCN, LHR SFO. ended up costing $4000 for the two of us on British Airways. Flying non stop.
Could have done it a bit cheaper, but I certainly didn't want the hassles of hop, skipping and jumping my way there.
Fortunately for me, I had enough BA points to get my pre and post cruise nights for free. Not fancy, but at least free.