Methinks you're confusing a split with a consolidation.
WMT are doing a consolidation - so for every 10 shares you now own, you will own 1, but it will be worth 10 times as much per share.
And if you want to buy back in after 5th May, you will only need to buy 1/10 of the number of shares. If the price per share doesn't change (10 x the current price) then it will cost you the same.