I've currently got the free Nexus deployed, and there are various infelicities involving authentication and staging. I am really allergic to buying a tool with a one-year term license where the price could go up arbitrarily in a year. Has anyone had success with any open source repo manager, or even one for money with a less frightening business model?
In my opinion, the "only" other decent alternative is Archiva (but Nexus is superior to all from a technical and user experience point of view). See the Best enterprise repository tool for Maven 2? question here on Stack Overflow for a summary of this point of view.
But, actually, my real suggestion would be to contact the guys at Sonatype.com to share your concerns and see if you can find a win-win solution with them.
In any case, choosing one repository or another doesn't really lock you in.
The whole world of software seems to be going the SAAS / subscription model these days, so this is the first I've heard of it being called frightening. In fact, having to pay a full price up front with no recourse in future years as your needs change is even more frightening imo.
Since there is an OSS Nexus, you hardly get locked in to the Pro version. If you don't find the price to be justifiable given the feature set, then you simply don't renew and continue to use the OSS verison. Naturally it's in our (Sonatype's) best interest to ensure that the price and features justify renewals as time goes on. It means we both have skin in the game.