I am coming late to this discussion. Sorry.
I have an FNX-40. Great gun, very accurate and easy to shoot. I carefully compared it to the Sig SP2022 and chose the FN, but both were very fine, and I could have been happy with either. The FN seemed to fit me better. I forgot the exact price I paid, but it was about $75 more than the Glock 22 on the shelf. I tend to use Glock 17 / 22 as a common price point, and I rate every pistol in terms of "more pricey than glock" or "less pricey than glock"... the FNX was more by about $75.
At its price, I thought the FNX was a bargain. It was equal to pistols costing several hundred more.
As far as that intangible attribute "build quality", it is hard to judge objectively. Obviously, if you let a group of people handle a kel-tec PF11 and a Les Baer 1911 side by side, everyone is going to judge the kel-tec as lower "build quality". But with more closely matched pistols, it gets very subjective.
With that said, my FNX "build quality" I would rate as slightly superior to my several glocks, superior to my wifes LC9, and about the same as my walther pps. Based on shooting a Sig 229, I would rate it equal. Based on shooting a Beretta M9 I would rate it equal. Based on shooting a Ruger SR9c I would rate the FNX as slightly better. Based on shooting a 1960's BHP I would say the BHP was superior. Based on shooting a Walther P99, the nod goes to the Walther. Based on shooting a colt python, no comparison.
I seriously question the judgment of anyone who says that the FNX is overpriced based on how it compares to other pistols.
Jim