Pretty much any z170 motherboard would work. This one looks decent, but if you look you can find some as cheap as $100.
https://pcpartpicker.com/product/qJbkcf/msi-motherboard-z170apcmate
Seeing as you want budget parts, it'd be a good idea to get an i5-6600k if all you're doing is gaming. You won't get too many benefits from an i7 unless you're doing something like rendering. Plus, it'll give you money to get 16 GB of RAM instead of 8. If you don't plan on overclocking, you could even get a non k CPU. You'd only need the stock cooler, meaning you won't have to buy a separate one, and you could opt for a cheaper motherboard that doesn't support overclocking.