The K versions often have similar, sometimes even lower prices than non-K, just because of competition pricing. The K normally have higher boosts. The K don't just overclock, but when paired on a Z board offer the full range of settings to adjust the cpu where the non-K don't. The K versions almost always carry a higher resale value due to demand.
Unless there's a solid reason, like 3rd Party bios incompatibility (Dell, Lenovo, HP etc) it's usually overall beneficial to go with a K.
10700k : $394, 10700 : $318. $76 difference.
4790k : $150, 4790 : $61. $89 difference.
You'll get the difference back, $± on resale, but get to have the benefits during ownership for overall difference of $0 ±.