I'm trying to add conditional logic to a paypal field

You were almost there. Just a few changes needed:

1. Add one Form calculation field that will receive result from Conditions you already made:

So you will do that for both conditions.

2. Then, in PayPal wizard change Get price from to be your calculation field:

That's it, that will do the calculations as you wish. You can also make your calculation field hidden since it is not necessary for your customers to see it.

If you have further questions please let us know.

Thank you!