Might it be cheaper to fly from the US to UK then WizzAir from UK to Krakow?
Possibly but if so I'd ship your bags on fdx, ups or dhl to simplify you catching your connecting flight (delays, etc), security screening, etc. For the den-lhr leg check out orbitz, travelocity and kayak. Low cost carriers such as southwest, wizair, etc usually don't participate in those websites so go straight to their own portals once you check out the us-uk connection.
Remember -> the fewer bags you have -> the lower chance of a heart attack! ;) Ship it a day or so earlier, get a tracking number and forget it.