There's no charge for downloading and printing scores and parts, so if you wish to make a donation to charity I would suggest £3 to £5 or equivalent in local currency. My preferred charity is Alzheimer's UK: you can link here.
If you would prefer to donate to another charity, there's a list at http://www.charitychoice.co.uk
I have for sale some scores, books and CDs related to completed research. If you are interested in the orchestral music of Malcolm Arnold or William Alwyn you might find something of interest here