The cost of an ID card may be $15 but you have to apply in person at a DMV with two legally acceptable documents showing your legal name and birth date, plus proof of residence, plus proof of Social Security number. So if you live in a village it's now $15 plus the cost of a plane ticket to a DMV plus the difficulty of obtaining those documents especially for the older generation. Plus hassle. Lots of people would rather not vote than spend hours at a DMV.

A lot of reasonable-sounding laws like this are actually ways to suppress a particular group's vote. If you can inconvenience a group enough that even 10% of them can't vote, that can have a pretty big effect. For example, a proposed law (in TX I believe) would not allow people to vote if their last name on their ID did not match their current last name. Sounds reasonable on the surface, but who is most likely to have a last name which doesn't match? Recently married women, and of course that demographic tends to vote Democrat.