Latvivian Automobile Federation have discount code on Stena Line to com to NEZ event Nynäshamn-Ventspils-Nynäshamn:

Stena Line reservations must be made through e-mail Den här e-postadressen skyddas mot spambots. Du måste tillåta JavaScript för att se den. requesting with discount code NEZ Event NEZ20. With this code you should receive 20% discount.

You can also travel with Tallink to Riga and you can use discount code:

Tallink code: 94531