The only way I have ever had a coin slabbed is to submit through a local dealer. The main benefit is not having to join the club. Also, it never hurts to have a second set of eyes to look the coin over for any problems (scratches, cleaning, ect.). Likely, the dealer has coins of their own they are submitting, so your coin can "ride" in the same box as theirs - saving a bit on shipping. I've done this numerous times with dealers I have a rapport with.
I'm a Collector's Club member and an ANA member so I can submit to either, although my OCD requires me to use PCGS since that's what I already have all my slabbed coins through.