Minimums vary by site, but most start around $10 or $20.
https://debate.socialism.nl/forum/showthread.php?tid=105645
http://forum3.bandingklub.cz/viewtopic.php?f=29&t=1350162
http://horsecity.ru/phpBB3/viewtopic.php?f=33&t=186827
https://mmomakemoneyonline.net/threads/online-casino-s-registracnim-bonusem-ceske-casino-paysafecard.374645/
http://horsecity.ru/phpBB3/viewtopic.php?f=8&t=326139
http://forums.indexrise.com/thread-708849.html
http://ewmen.com/viewtopic.php?p=935290#p935290
https://mmomakemoneyonline.net/threads/online-casino-licentie-nederland-ook-gokautomaat-online.543787/
https://debate.socialism.nl/forum/showthread.php?tid=196851
https://neoternia.net/viewtopic.php?t=358475
https://mmomakemoneyonline.net/threads/minimum-bidrag-for-online-casino-casino-online-gjennom-overforing-swiss-casino.502708/
https://www.ww2.site/forum/viewtopic.php?t=92046