I have a Kawasaki 2004 KLX 110. It is a four stroke and in good condition. The only things wrong with it are that the handgrips a worn and there is a small piece of plastic missing around the chain, but it still runs great.
I just bought a similar bike, 2005 Honda 100cc 4 stroke, two months ago. I paid 1,600 and that was the standard price I was seeing for these types of bikes on the market. But mine was in almost new condition and didn't need any repairs or replacements. Hope this helps and good luck!