Here is a list of stuff and Part Numbers you would need to rebuild the top. Also you need to check the water pump and oil pump while you are doing this just to be safe.
13008-s008 - Ring Set - $31.86
11004-s006 - Head Gasket - $19.82
11061-s069 - Gasket Head Cover - $16.68
92049-s006 - Valve Seals - (Need 4) $3.13ea - $12.52
11061-s076 - Exhaust Pipe Gasket $8.37
Total without shipping - $89.25
This is to do it yourself. I had mine done at a shop and I forgot how much I paid. I am having it done right now to my 05 KFX 700 which has 2 cylinders and it is costing me $905.00 with parts and Tax. They are changing the rings and Valve seals and cleaning valves and changing gaskets. If should be cheaper for you. I was thinking it cost me around $325 to 375 labor. Buy your own parts. OEM Parts. That is what I do.
Cheapest Part are at Partzilla.com - OEM Powersports Parts from Honda, Kawasaki Polaris, Suzuki and Yamaha at discounts up to 80% off MSRP