1 DVD-R seems to be about ~$1 whereas 1 4 GB flash drive seems to be ~$4. 4 GB SD cards seem to be about ~$5. DVDs are still cheaper apparently. By the way, any reason you can't use the internet to transfer the file; it's not just cost, but time. Unless you send many TB of data by post, it would likely be faster to just SFTP the files around?