Let's say a $50 minimum.
In the end, I think you interpreted pp's question correctly, but that the pronoun is "you" rather than "I" and the disclaimer "if you don't mind my asking" suggests that the question is how big is your donation budget. One answer to that is in the original post, $20k available for this offer. Another answer is here.
(The disclaimer seems to me to require a strong update, but my prior is even higher.)
Giving money to effective charities is one of the ways we can have the biggest positive impact in the world. If you've been thinking about giving to GiveWell's top-rated charity, the Against Malaria Foundation, but haven't gotten around to it, perhaps this will help: make a donation of up to $2K and I will match it 100%. I'll match up to $20K this way.
(Any money left over at the end of the year will also go to the AMF. That makes this a donor illusion, in that you're not actually affecting the amount I give them this year.)
I made the same offer on my blog