I don't think it's as big of an issue as you suggest. If you've spent umpteen hours developing the product, the amount of additional time and effort required to

I don't think it's as big of an issue as you suggest. If you've spent umpteen hours developing the product, the amount of additional time and effort required to put a simple discount system in place is negligible. You could even set up a standard response email. If someone writes asking for a discount, just send them a ~10% discount code. It should pay for itself in the form of (even slightly) increased conversions in no time.