If it's for a kaby lake cpu the Asus prime z270a is a good mid range board with plenty of features, but I've had my eye on the Strix z270e gaming because of its looks and features such as onboard wifi.
if it is too expensive then you may need to look into a mobo with a H270 or B250 chipset. but you wouldn't be able to overclock on those chip sets rendering the advantages of the 7700K useless