Conditional Cost Calculation & PayPal Standard

Hi all,
I have a form that has a radio selection list that I need to use to determine total cost for PayPal Standard payment. How do I go about setting this up so that:
index 0 = <amount a> index 1 =
index 2 = $

I think I can use the Product pricing field for this part, but, these values only need to apply if another field’s value is set to “Pay with PayPal”.

We’d like a discount field where if the value matches another value, an amount or percentage is subtracted.

Next, what’s the best way to set up being sent to PayPal for processing? Do I land the user on the standard confirmation page with a button to “Pay Now”? Or, can it go to PayPal first and then return to PayPal with all of the same conditional POST values I already have set up?

Lastly, I need to do this without spending any additional money. I’d love to subscribe to GravityPerks or buy the 1 time plugs, but I have no ability to do so or purchase Gravity Wiz Conditional Pricing or eCommerce Fields.

UPDATE:

I figured out the Coupon Add On.

I figured out to only enable the Feed if payment type is set to PayPal.

I figured out workaround for conditional calculation… but am still interested in other options.

Is there a way to automatically send a notification IF payment type is set to PayPal AND if Payment isn’t received or marked as complete after xx minutes? Currently, I have notifications going out when the form is submitted, but since the PayPal checkout wouldn’t be complete yet, I set up ANOTHER notification for Payment Complete event. This works OK, but what do I do about scenarios when someone is directed to PayPal and they don’t complete checkout OR what happens if they don’t click “Return to Merchant”? Is that important?

I don’t have users logging into the site to check payment status, so right now they would just need to check to make sure they receive TWO emails for PayPal payment orders.

Lastly, if they do not complete checkout, is it possible to email the customer a link to PayPal checkout completion?