The total basis is still the same. You just have a different number of shares.
If your basis was 30 dollars per share before and it split 2-for-1, then your new per-share basis is 15 dollars.
If you have the same brokerage, the cost basis should be adjusted after the stock split.
If you can provide more information, I can check into it.
assuming the split resulted in more shares of the same stock, your tax basis per share is what you originally paid divided by the total number of shares. so if you paid $500 for 100 shares and got an addition 100 shares the cost/share is $500/200