shipping m/c parts

Ok I know someone out there must have done it.

I've picked up a few parts whilst over here in the uk.... an almost complete motor for example and need to know anybody know of the cheapest way to get this stuff home???? the quotes i've been getting are pretty over the top $$ wise and whilst I can carry it I don't think the airline would like it if I was to take it as carry on.... any suggestions.

Cheers Rob

sea freight? would take 6-8 weeks but might be cheaper?
excess luggage on the plane? ie. put in suitcase & pay the excess?