Disclosure, I work at Dropbox: but did you consider paying for a tool? Or were you mostly interested in free options?
Paying for extra space seemed overkill, given that this was literally a one-time P2P file transfer. I really should just be able to send a file to another IP address without having to pay for storage somewhere.
https://serverfault.com/questions/53531/copy-large-file-from...
Sorry to keep bike shedding this!