Prices for CBXes have gone up in the last two years. You will not find a decent running bike anymore for under 5,000.- regardless of year.
Considering conditions of 1-5, with 1 being the best, the ball park prices for a 2-3 condition bike are: (IN THE U.S.!)
1979 - 8-10K
1980 - 7.5-9.5K
1981 - 6.5-8k
1982 - 6-7.5k
Key items are paint condition and exhaust.
Feel free to argue with me. I have bought and sold around 15 CBXes over the last 18 months of basically all model years. None of them on ebay!