Real life pricing isn't the same as Minecraft plugins. They may be free or max $10 a piece, XenForo is the entry into a bigger reality. It's at the bottom of the bigger reality, I personally think they should charge at least double. It's better than IPB... and cheaper...?
Well, let's see, I paid around $175 for base IPS forum with $25 6 month renewals required for support or ability to download any of your existing versions (you can't let it lapse and download versions up to your support expiry)
WBB was around $90, but required several add-ons to get to where I was with XenForo - and the "new version upgrade" is different than XenForo's process.
If the paid scripts are to expensive, I'd encourage you to start with one of the free ones to see if your site takes off - just be sure that there is a conversion path for whatever one you select to other scripts you may be interested in if your site takes off.