They charge 500rmb per day for the overstay at the border when you try to go out. That's almost 100CAD
You must pay in CASH only
Processing time is 30min, so if you have a flight to catch make sure you go early (I had to rebook a flight even theoretically I could have made it, they weren't nice about it)
But they told me if it's your first time they tend to let you go (Funny enough this did happen to me before aka it's not my first time. The first time i overstayed by like 15 days so they only calculated 5 days, still it's a very hefty fee)
I tried to reapply for a Chinese visa in Hong Kong, however the lady at the HK officer told me I had to go back to my home country to apply since I ticked yes to the "overstay" question on the application form and by law I won't be able to reapply in Hong kong...