Should I mention my interest in teaching in SOP and recommendation letter?
For a SOP, you may mention something about your desire to teach. However, I think at most higher-ranking economics departments, this would not be viewed as positively as having a strong research interest and agenda. You may gain a small benefit if the reader of the SOP gets the sense that you are a "team player" who will do a good job TAing and not make a fuss about it. 

(I will note here that my advisor has told me that some faculty are extra  suspicious about investing effort when they hear too much discussion of teaching from a woman - they already think of women as being less serious about research because of biases and discussion of teaching by a woman can support their stereotypes. So note this if you are a woman.)

I would say that it is not inappropriate to talk to your recommenders about your desire to teach economics. However, I would tend to frame it as and interest IN ADDITION TO research. You can say, I really see myself ending up at an institution that combines teaching with research - what would you recommend I do at this point to make myself the most competitive for those types of places?