How much are the parking options overnight near the new Pedwest crossing at San Ysidro? The Las Americas outlets are located close by. Would it be possible to park there for free?
Paid overnight parking typically provides some security, you won't get that from free parking. As far as I am aware there are no free parking lots in San Ysidro, I believe the overnight rates are around $25+ per night.
There is limited street parking around San Ysidro, but it'll be unsecure so at your risk.
I can't answer about parking at Las Americas Outlets, but I would speculate that being so close to Pedwest they would probably limit your parking options at the mall.
If it's an option you could park further north into San Diego and take the trolley (Blue line) to San Ysidro. This may provide cheaper parking options further from the border.