Most Embassies strongly emphasize that error in the personal data from the passport, will lead to rejection, and can not be changed neither by you or the Embassy.
You need to write it excactly as in the machine readable field, at the bottom of the picturepage in the passport.
Best country to apply in, is your homecountry, where they will be familiar with the documents supplied for the application.
It is 500.000 bath each depending on Embassy.
Scroll or search all the great answers allready found in the group.
Anonymous users should really do their homework, and read previous posts, when they are not suppotting the group as full contributing members of the group.
If you don’t have the nerves, and are able to change travelplans, when a Immigration Officer deny you entry to Thailand, you could choose the multi entry tourist visa.
Read all about it in the visa section of the Thai Embassy closest to you.