This post is part of the series on Balsamiq Mockups 3.
Mockups 3 for Desktop is a one time purchase and there are no maintenance costs for the license; in addition, licenses are tied to humans and not a particular machine so you can work on it on a desktop and laptop with the same license. A single user license currently costs $89.99, but there are volume licenses available with discounts starting at 5 users and increase with volume.
I use the desktop version as I often work offline (when travelling and on dodgy WiFi) and don't like recurring subscriptions.
With the desktop license, minor-version updates are also free (so 3.2, 3.3, etc.) and there are no maintenance or renewal costs to keep using the software; major-version updates will have an additional cost, but as updates are not required, you will be able to continue to use version 3 if you don't wish to purchase a major version update.