The article Nick pointed out is pretty much on the spot.
I get a lot of questions regarding how a person should choose a dojo due to the dojo search engine here on this site. I usually tell them that it's definitely worth it to go check out all of the dojo in the vicinity and not just the closest one.
Check to see if you like the teacher. See if you think you would fit in with the students. See how the teacher acts towards the students. Watch how the students act toward the teacher and towards the other students.
As far as the money issue goes, my experience has been that monthly dues range from US$20 up to US$100 and above. The average that I've personally experienced has been about US$70/month, though.
As we say in Japan, "Rather one spend three years looking for a good teacher than three years studying with a bad one." I might substitue "school" for "teacher," though...