Dear Magister, you philosophy is admirable but as you know the ideas do not feed the body.
In my opinion to ask for example 4 $ a year to people who participate in the Letters to the Devil Members area will not change substantially your policy. Instead my opinion is that to put a donate button may confuse us with the others religious groups. With donations, people think to acquire rights for donating and besides, what frequently starts as a free donation becomes a donation with a not stated but very high minimum amount, like here it happens in the hospitals to the nurses.
It is not against the Satanic attitude to be compensated for a service. With a little annual payment we all will be happy and you will have a little contribution at least for the server cost. You have to pay bills, in spite of your philosophy. A grotto has a balance and the members pay the expenses, but your online grotto is totally free.
I agree that our activity should not produce extra money but I do not see anything bad in paying the expenses, as everything we buy has a price.
Think about it Magister.