I have a zen site with a customized quantity factor.

TP = total price
BP = base price
Q1+Q2 = quantities

This formula is how totals are calulated on the site:

TP = BP + (Q1 x BP) + ((Q2 - 1) x BP)

according to my calculations, zeros will conform to this method as well.

TP = BP + (0xBP) + (-1BP) = 0
The idea here, is that we need to enable the customer to choose a zero quantity for either one of these fields. (but not both)

This method works for the most part - but I am concerned about potential ZERO orders being processed.

if both quantities are set to zero, the order total will be zero - but since it's set with attributes, it seems to me that this order would try to process - leaving a record of a purchase where the quantities and totals are both zero.

Not sure what paypal would do with that, if anything, but I would like to block processing of any order with a zero total, perhaps generating an error code.

Is there any existing contribution that will do this, or does anyone have some ideas?

Thanks in advance,