My buddy Andy routinely ships his mountain bike box by FedEx. He was astonished how much easier and cost effective it was than trying to send it as luggage.
… Consider: a single 25-pound suitcase or shipment from Boston to San Francisco by FedEx Ground costs about $31 vs. $23-$25 on Delta or nothing on Southwest.
But once that suitcase weighs over 50 pounds, excess charges kick in on the airlines, even on Southwest: you’d pay $56 for a 55-lb. bag using USPS on that same Boston-San Francisco trip, but twice that on Delta, which adds an extra $90 fee each way for bags weighing over 50 pounds. Even Southwest will charge you $50 each way.
And if your bag is both heavy and oversized (larger than 61-62 linear inches), you’ll get hit with triple jeopardy on some airlines: a fee for the first bag, plus an overweight fee, plus an oversized fee. Such a bag might cost nearly $300 on Delta on a trip from Los Angeles to Seattle vs. under $40 via FedEx Ground. …
airfarewatchdog – Airline baggage fees chart, updated
more – Trick, repack and rethink your way around the new luggage fees
=== UPDATE from Dana:
When I came back to Vegas after 4.5 months in Canada, I used Canada post to send my extra bags. It cost me $170 CAD. Had I flown with the bags (5 extra) it would have cost me $725 on ScAir Canada/United. They also charged me an extra $10 per bag that I was traveling with, because I didn’t check in on line. Which you are not able to do when traveling with an infant. What a crock.
ps – my bags arrived in 8 days
Rick McCharles 
When I came back to Vegas after 4.5 months in Canada, I used Canada post to send my extra bags. It cost me $170 CAD. Had I flown with the bags (5 extra) it would have cost me $725 on ScAir Canada/United. They also charged me an extra $10 per bag that I was traveling with, because I didn’t check in on line. Which you are not able to do when traveling with an infant. What a crock.
ps – my bags arrived in 8 days