I'm filipina domestic helper her in hk. How I can get a one day shenzhen visa and how much is cost.

You just need to go to the Luohu Port to apply for it with your valid passport, a small application form, a recent taken photo and fee of 168RMB.

Personally speaking, it is not assured that you can get it at the border. So if possible, you are suggested to apply a single entry Tourist L to Shenzhen in advance.