Subscription to 1Password is not mandatory. Or at least it was not in the past. Without a subscription, you can create local vaults which can be synced via Dropbox, iCloud or over WiFi within the same subnet (which means over VPN too). Here is some documentation on the Dropbox sync for example: https://support.1password.com/sync-with-dropbox/
I can't find how to purchase the single license for Windows. I found the download for Windows v4 and the single license purchase for Mac here: https://agilebits.com/store but not the Windows license.
Funny enough, 1P6 worked fine with my local/Dropbox vault during beta, then the app stopped letting me update my vault when it left beta. :\