normal and the unique rings drop from normal webshop strongboxes.
season rings drop from the seasoned strongboxes you have to loot or buy from other looters.
webshop [strongboxes + key] cost 1 US$ each and guarantee 10 ped TT content.
webshop [keys] are needed to open looted or bought season strongboxes and cost 1 US$, too.
plus the costs for the seasoned stronbox, if you buy them from players.
so you pay more than 1 US$ to have and open a seasoned strongbox, but still only get 10 ped TT guaranteed. 150% for gambling on a season ring.