In my years of bringing things in for charity, I found that it didn't matter what you paid for an item - receipt or no receipt. I brought in a generic projector bulb that was about a third the cost of a name brand bulb. Didn't matter - the value in their "book" on a projector bulb is all that mattered. That is how they assessed the duty - not on my receipt. So be ready for a big hit on the PS if you choose to declare.