is seeing as I'm unlikely to get any more than "up to" 76Mbps from my ISP's fibre anyway,
Effectively any hardware that still boots will work as a home router. A 500mhz Pentium III with 64mb ram can handle a 100mbps connection without breaking a sweat.
Decide what you want to do about a fileserver first, that's the deciding factor for hardware.
CuBox armv7 without having to be too inventive and using binary blobs from odd places for bootloaders and whatnot
Do be aware that i386 and amd64 are the more tested platforms by a wide margin. The further you go into niche territory the more stuff will stop working and the more you'll have to mess around.
and what good deals there are,
I spent rather more on a mini-ITX PC system with a loud fan
Again, home router duties require negligible horsepower. If you don't need much from the fileserver front you can probably build a machine from parts in your basement (can't beat free), or you could easily get away with a lower cost low power passively-cooled itx system.
