[mchannon]

Here's a wacky idea: say no. Don't offer a perpetual license.

Alternatively, you can price it so high that a 1% money market account earns exactly X in interest in perpetuity.

With a perpetual, you lose autonomy. You will be forever unable to discontinue your product should it stop being profitable or worthwhile or relevant. When that day finally comes (you pass away at the tender age of 108) this client might be ticked off and demand a refund plus interest from your estate.

[AnimalMuppet]

I'd say price it higher than that. Price it high enough that they clearly don't want it. But if they do want it, it's a price that you would be deliriously happy with.

One thing to keep in mind, though: If they have a perpetual license, they may want much more of your service. If you have to provide that, your costs may go up.