Just as a useful point - United charge $100 extra for any bags over 2 per person (50 lbs limit per bag). This seems quite cheap to me to ship 50 lbs of stuff over?
After pricing what it'd cost to ship my belongings (clothes, a few books and dvds, cat stuff, other personal items - no furniture or anything) via the post office or through a shipping company like upackweship, we realized that it was actually going to be cheaper to buy an extra plane ticket and pay to carry over a few extra bags! So we did - it was $600 for the ticket and $200 total for the baggage - I flew Delta with a laptop carryon and four bags weighing 40-50lbs each, so paid $100 each for bags #3 and #4 - and then spent the next couple of days unpacking, so that there'd be less to do when I arrived for good.
I took a couple of the empty bags back with me, repacked them, and flew BA (which isn't dropping their baggage limit from 70lbs to 50lbs until after the new year) over in October when I moved for good with my cats - this time I had two large bags (58lbs and 63lbs, I think), one small carryon suitcase and my laptop bag, and didn't pay any extra charges. Both times, I walked through the green customs channel with no problems - since I was moving my used household goods for purposes of resettlement, I wasn't liable to pay any duty on my belongings.
If there's going to be two of y'all flying, and you're trying to transport a similar amount of stuff (300-400lbs, and all of a size that'll fit in a suitcase), I'd seriously recommend doing the same thing - I didn't have to fill out any customs forms, since my belongings were accompanied, and I didn't have to worry about my stuff getting lost (except for the ever-present worry of lost luggage). It was fantastic being able to pack my bags the night before, fly over, drive home from the airport and have my stuff already at hand. And it only cost $800 extra - $600 for the extra flight, resulting in a week in the UK getting things unpacked and settled, plus $200 total on top of regular baggage allowances for about 400lbs of stuff. We also wound up shipping one box via airmail - 50lbs was $198, and would have been over $100 if we'd shipped it surface mail (6-8 weeks), so we figured $100 for 50lbs and "overnight" service was a deal.
