It doesn't list the price, but I can tell you from experience that a new one from Napa at retail price was around $120 a few years ago. If you're looking for a used one, I believe the 2.8 and 3.1 share the same regulator. Hit up www.car-part.com
and look for a fuel injector, and that same vehicle should have a fuel pressure regulator as well. I paid $75 for a full rail, six injectors, and a fuel pressure regulator from a junkyard.
Now that I think of it, I might still have that used FPR sitting at home somewhere. I only needed the injectors, and I'm pretty sure I kept the extra parts. I'll have to check around tomorrow when I find time and see if I can't grab it for you.