Kodai goes for max 5k right now, never 10k. I sold mine for 3,5k because it took a while for me to try to sell it for 5.
Btw the price of the kodai won't go back to 20-30k because it's really easy to get one right now. It takes around 6 hours to get the points to buy one, if you have some luck you will also get one as a drop in those 1000 kills. No way it will be 20-30k.