Free trial not that free

Using a 100% off promotion code still requires a PayPal login and sends an email saying the user has subscribed to an $x per month plan. Can this be circumvented?

If the plan only allows recurring subscriptions then no. What it's doing is setting up auto recurring payments at PayPal so when the free trial ends they're automatically renewed. If you allow single payments I believe it won't do that anymore.

K. Consider that a feature request, then--at least a confirm that they won't be charged maybe. I'm also not seeing the promo code work at all. I'm charging myself a small fortune testing the site

If the promo code isn't working then that likely explains the issue. Normally they would instantly activate and never see PayPal except in situations of $0 initial price duration with a regular price and duration while only allowing recurring subscriptions. In the case that they're charged nothing at PayPal it will be very clear to them on their PayPal payment page that they're being charged for nothing and that in XYZ duration they'll be charged XYZ price.

I'm charging myself a small fortune testing the site

That's what PayPal Sandbox is for. It uses dummy accounts so no money exchanges hands, but allows you to setup configuration and get a feel for things. Getting used to the sandbox interface is a little daunting, but it's very helpful for making test purchases.