Pacer took thinking about nuclear fuels in a lot of new and interesting directions. For the use case of interest, they really wanted to maximize the fusion yield fraction, minimize the radioactive products, and minimize the total yield. Had it ever been allowed to proceed to a commercial scale, these would have been very tight, very challenging, technical constraints.

If you relax one of those requirements, then it becomes instantly clear that limitless cheap energy is possible. For a somewhat absurd example, imagine that we build Pacer plants in space instead of on Earth. There's no longer any size constraint on the blast chamber. You can go to triple-stage (like Tzar Bomba) or more designs, at which point the fusion fraction gets extremely close to 100%, and the cost per unit energy becomes somewhat hard to fathom. But on Earth, it still would have been expensive.