For 20 rolls, you could probably send for processing anywhere in the world, and the postage will be an insignificant part of the cost. I'd probably find a cheap pro in the USA and send it there. I'm not from the USA, but they'll always be cheaper than Australia, or the UK or whatever. Send it with tracking there and back, I doubt you'll have any issues. I've had Kodachrome processed in the USA, and I'm in the UK, no big deal really.