Livius.org is a not-for-profit project run by Livius Onderwijs, a private school in the Netherlands. It will always be free. If you want to take a share in the costs, you can donate money to the Stichting Wetenschapsvoorlichting Oudheid, a small foundation that supports the improvement of science education. It has in the past supported Livius.org and several other small projects.
Stichting Wetenschapsvoorlichting Oudheid
The Hague, The Netherlands
The account number is IBAN NL25 INGB 0006 2904 08; BIC/SWIFT INGBNL2A.
Thank you very much.