Cheapest of cheapest worth having ?
if it's gaming box, be aware that staring with Z170, Asus started slipping in substandard audio solutions in all their boards below $150 .... with Z270, other manufacturers have followed suit. As you should expect, cutting cost means cutting component quality. So you don't wanna cut too much and then find out you got less than expected. For most gamers, that's going to mean avoiding ALC 887 / 892 or Supreme whatever that is relabled ALC 887 / 892. The gaming standard is ALC 1150 or the newer ALC 1220
Anandtech wrote that the new baseline in the Z170 MoBo category was the MSI Z170 SLI Plus
http://www.anandtech.com/show/10236/the-msi-z170a-sli-plus-review
This carries thru to the Z270 series as it has the best balance of price and component quality that i have seen so far.
MSI Z270 SLI Plus w/ ALC1220 Codec ($132)
http://pcpartpicker.com/product/G9X2FT/msi-z270-sli-plus-atx-lga1151-motherboard-z270-sli-plus
MSI Z270 SLI w/ ALC1220 Codec ($130)
http://pcpartpicker.com/product/gGtWGX/msi-z270-sli-atx-lga1151-motherboard-z270-sli
If you don't want to OC, I would go with an H170 board, not B250 which has limited storage options. Problem is, by the tome you get down below the 4130 price point at h170 and b250, you are still getting crappy audio solutions.
If this is a gaming box, as opposed to a workstation box I'd scrap the 7700k and save $90 - $100 with a 7600K, put it in a $130 motherboard and use the leftover bucks for a decent cooler which you don't seem to have accounted for since the k series doesn't come with one.