Update: Resolved the main issue, it turns out I simply did not have the form variable associated with the cart Price in the Add to Cart dialog.
One other thing though- I am using the Paypal Web Standards thing. The cart contents all transfer over to Paypal just fine. But during the checkout process, before it submits to PayPal, there's a form for the user to enter in all the user info - this does not get transferred to PayPal for when the user elects to chose to pay by credit card - the have to fill it in all over again. Should this be automatically sent to Paypal, or does it require extra coding?
Or can I just eliminate this form from the checkout process - and if so, are there any parts that must be retained, such as the email address?