AMD's official plans are for launching it in September, which more or less means quantity retail availability in mid-late Q4. Pricetags are anyone's guess, but it ain't gonna be cheap. Barton is taking the Duron title. I would venture to guess the lowend A64 would be around $400 at or a couple months following launch. Mobos, lacking memory controllers will supposedly be "cheaper" but nothing new in this industry ever is so boards should be $100-200. If you are using DDR SDRAM with your Celery, you should be able to use it in most if not all A64 boards.
Personally I would drop a P4 2.4b in the board and wait for the interesting stuff next year though 🙂