@Nils *****
be very careful with those agencies. A good friend used one for years to get a year-long, multi-entry non-B visa from the US every year when he went back.
Then one year the consulates stopped issuing them and he couldn't get ANY visa at all with the paperwork he'd got from the agency. When he got back here they wouldn't refund him one single baht.
Just be careful, if it sounds too good to be true or too easy it's fake