Got a link ? I thought this was so too but a quick look at DMV says the ID fee is the same as for a drivers' license.
Looks to me that you don't even need to prove citizenship in TX anyway, last four of SSN will do - and legal aliens will have that as well as citizens: All voters who registered to vote in Texas must provide a Texas driver's license number or personal identification number issued by the Texas Department of Public Safety or the last four digits of your social security number.
It’s written in the new picture ID law that it is free. This law hasn’t taken effect yet since Holder has the law in court. The ID info. you are reading doesn’t require a picture ID.