User friendly? I'm not saying this is the most secure way, but you could leverage DropBox, Box, OneDrive, etc.. Just share the root folder you want them to have access to using the web and drop your files in there. Done. You can automate it, too, by having your jobs drop the file in the appropriate folder. They can use any number of methods to get the file. Data at rest encryption would be handled by GPG if you even need it. You already need them to authenticate and you authorize the access. GPG would be an additional layer. It depends on how sensitive the data is and how much risk you want to accept. You could automate it pretty easily with some PowerShell. Additionally, you might need to purchase a business-class service from the service to stay within the bounds of the EULA, though.
If you want a more secure way you'll need to invest in a service of some sort for secure FTP that uses GPG for encrypting the files and/or PKI for authentication with ACLs to white list authorized businesses.