As others, I picked up suitcases/duffle bags from the thrift store and chucked them on arrival, on the way back we found some of those almost tarp like big plaid bags for a few bucks at a dollar type store and they managed for the trip back (may have has some duct tape assistance. helmets were carried on (fragile!).
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1 Super Record bike, 1 Nuovo Record bike, 1 Pista, 1 Road, 1 Cyclocross/Allrounder, 1 MTB, 1 Touring, 1 Fixed gear