Having got my Thai wife here i can tell you its ruddy expensive. My advice get her over the English Channel in one of the many boats, its much cheaper. Then you get everything for free.
Go on your countries Thai Embassy web site and look under the visa section. There are ofcourse many many different visas all explained there. Look for Non Immigrant O long stay visas, O-A 1 year and O-X 5 year
thats my worry Stuart. It may just be easier to show a cheap outbound flight to cambodia or similar. Just my luck to get a jobsworth at the check in desk