[jgeorge]

Have you looked at the Intel Galileo? It's a singleboard computer, and can run something Debian-ish. The stock Intel software is very scaled down busybox, but I'm pretty sure there's a full Debian variant for it, I haven't looked in a while. It supports PCI Express mini cards, and there are a couple of Wifi adapters that should work (AC7260 for example).

The cost is a bit higher than a Pi (The Galileo would be around $79 and the wifi card another $30 or so) but still far cheaper than kitting up a NUC.

I'm rather fond of the NUCs, they're not the cheapest things in the world for the size, but you do have quite a bit more flexibility since it's a full-on PC at that point and not a SBC.