I have asked my friend about this word before , He also said it means thanks or appreciation .
But when I used Eyvallah on a chat with a turkish friend , she said I used it wrong ...
I am still confusing about it , too ... :)
I found it some english meanings of Eyvallah in a dictionary :
eyvallah Thanks!/Thanks a lot!
eyvallah good-by
eyvallah so be it
eyvallah (informal) thanks
eyvallah bye
Eyvallah ta
eyvallah okay!
eyvallah thanks!
eyvallah all right!
eyvallah Good-bye!
eyvallah Thanks!, Ta!, Cheers!; Good-bye!, Cheers!, Cheerio; Okay!, All right!
eyvallah cheerio
eyvallah So be it./If you say so