We will be setting up a forum soon.
I was going to run XenForo on it, but it's gotten so expensive to purchase all the add-ons that I was contemplating for use since the script itself is so bare-bones comparied to other paid scripts that I am looking at alternative solutions.

Honestly... for what it costs to get XenForo to the equivalent of other paid forum script providers, I have to wonder why anyone would contemplate it currently. The other paid scripts offer so much more in their base core offering than XenForo does. The XenForo developers are HEAVILY reliant upon outside 3rd party developers (which regularly disappear) to bring their script up to any quality ability, and they are "loud and proud" on the fact that they are simply a "base" forum provider.

I would gladly use Invision Community.. but they have already warned that after this next version they probably won't support their current self-hosted script. With the number of sites I run (at no cost for access) an SaaS solution is a no-go, which is what their future game plan apparently is.

So we are still evaluating what to use. We really want to use a PHP based script as to do otherwise will realistically result in having to set up another server if it's not PHP based.
We are currently leaning towards SMF since a forum configuration would probably be better.
But an alternative is WordPress with one of the forum add-ons installed.