Same story from the GOP playbook...
These policies are not about "saving money", they are all about appealing to the GOP base.
The GOP sells their base the lie that "the poor (read: brown people) are coming for you". The poor are shiftless moochers who are too lazy to work and are taking advantage of "hard working Real Americans(tm) (read: whites)". So programs like this exist to help bolster the lie.
In the GOP playbook, money on drug testing is not a waste for two good reasons: 1) The 2 or 3 actual cases they find are "proof" that will be bandied about on the far-right talking circuit. It doesn't matter how many millions are spent finding the two or three cases... and 2) The money will be taken from other services so when those services fail it will be "proof" of how the government doesn't work.
And if any of the GOP donors can skim a few easy millions off top its just icing on the cake.