you don't want something too cheap since you are going for an i7 8700k you need a good motherboard to go well with that. something like ASUS ROG STRIX Z370-H or ASUS ROG STRIX Z370-F. will do be just fine and the price is reasonable for both 150-200USD.
for the rams you will have to specify what kind of user you are. if gaming for example you will have to specify what resolution and frames are you going for.
you will also have to give us full system specs.