SD cards electrical specification
I get the feeling that you do not understand these datesheets.

That 250 VAC is what the connector can survive without getting damaged. It does not mean that it needs 250 VAC to work !

Not even going into your 70V remark (too irrelevant).

An SD card connector takes an SD card and connects it to a chip (that could be a SoC) with an SD card interface. That's it. You need to think about what a connector does. It connects, that is it.

So just pick a connector that fits your needs (size wise and price wise), ignore the electrical specs as it does not matter.