This question is actually answered already on the FAQ page of the Choralia website under “What’s the reasonable amount of a donation?”, which reads:

Donations from individuals are typically in the 5 – 50 Euro range for each work. Choirs typically collect donations from several singers, so donations are typically in the 20 – 200 Euro range.

The proposed range is quite large because sometimes works are relatively small and include one piece only (for example, most motets have these characteristics), while other works include many movements and they are much larger (for example, oratorios). So, one can adopt the lower values for very simple and small works, and the higher values for very complex and large works.

This also somehow relates to the use of the “ads-stop” code, which allows to turn advertisements off on Choralplayer. The larger is the amount of the donation, the larger is the number of ads-free accesses assigned to the ads-stop code that you receive. Larger works will likely require a larger number of accesses in order to learn all pieces, so a larger donation is also convenient to obtain a sufficient number of accesses. Anyway, you can start with a smaller donation if you like, and make another donation if you find that the initial donation was not large enough to obtain the number of ads-free accesses that you need. Donations are associated to the email address of the donor, so, if you specify the same email address when donating, no new ads-stop code will be created and your existing ads-stop code will be updated with the additional accesses, so you will not need to manage two (or more) codes.

If you make one donation on behalf of several singers, you can share the resulting ads-stop code with the other singers, so that they can all gain ads-free access to Choralplayer. Alternatively, you may contact Choralia and request that the whole amount of the donation is divided into sub-donations associated to the individual email addresses of the various singers. You will have to specify the individual email addresses and the way the whole amount has to be assigned to the individual email addresses.