The lack of quality from Kumho was restricted to their entry level and first run tires, and is in the past…don’t know where you got that opinion. Kumho makes excellent tires for the money in all categories now, and Hankook makes great R-compound tires, but their street tires leave a bit to be desired.
Take a look at the Kumho AST, ASX, and the MX if you want a cost efficient summer tire. Another tire to look at are the Falken Ziex 912, cheap and performs decently. Being on 18’s your prices are obviously going to be pretty high, but Tirerack, DiscountTire Direct, and Vulcan Tire have great deals on the above.