I've been into my brakes a few times...
The wheel cylinders are, from my dealer, $130 each. Check in the parts thread in this Kawasaki forum for other prices.
there are some chinese ones on amazon for about $50 I think.
once you get into the drum you can determine if the shoes need replaced. They might just need adjusted. Although brake fluid is kind of acidic and might eat away at the shoe material.
it's fairly simple. The rear ones have the E brake cable, so that's 1 extra thing to look after.
I would recommend buying a shop manual. I have one, I can post the page instructions here if you want me too.