If an ID costs $30 and blacks are less likely to have $30 and a spare couple hours to get the ID, and blacks are more likely to vote against you if they do vote, by requiring ID you’re swaying the vote in your favor. Does this specifically affect every black worse than every white? Of course not.
This reminds me of the hazing of a ‘twenty-four hour waiting period’ for women wanting to obtain abortions. They know that women won’t want to come to the clinic twice (and stay overnight at a hotel if they are from out of town). They gradually make it harder and harder to make it to the clinics. Here they are making it harder to get a voter ID card by charging money for it (and you know there will be long lines). This voter ID measure is also a way to confuse voters (especially first-time voters who aren’t sure of all the regulations and procedures)
And yes, I know that this measure speaks more to the economic class of a voter than their ethnicity but this is in the same vein as the poll-taxes of days gone by and the GOP know they lost black voters during Katrina.