I just found that tab again, and saw that the "XenForo License" price was $160. Then it changed almost immediately back to $195. Huh? So I hit F5, and you can see it load "Total $160.00" then immediately $195 again.
First I thought it was VAT, but they display prices excluding VAT. Here's the first request to the page:
I think they just show a default value of $160, because on init an updateTotals function is called aggregating the prices of the base license with the selected extras (which updates the 160 to 195):
So... no price change, just weird UX. A default price of 0 would be saner (albeit also wrong) - or even a text "Calculating..." to make it look less like an error.