5 speeds are getting pretty expensive in the US also. Most likely that's because they're a popular conversion for Austin Healey Sprites and MG Midgets.
60A on ebay USThe 63A is a bit less expensive on the whole but also less frequently seen on Ebay.
63A on ebay USWhether these prices are a good indication of what you need to pay if you can find a gearbox I don't know, but they certainly make Australian prices cheaper than bringing a box from the US. New Zealand is probably the best option.