You can get a windows7 tablet on ebay for about $300.
Quote from Trader13:
I strongly advise that your trading laptop/netbook runs Windows 7/8. Your software choices will be severely limited with any other OS platform.
Quote from lwlee:
But you probably get what you pay for. 1.3-1.5lb, .5in thickness, at least 9in screen, long battery life, etc. The bar has been raised for tablets. The newest stuff coming out will probably only be worthwhile.