It depends on if you are comfortable or if whoever is helping you is comfortable with putting that stuff inside your ear. I am not so I went with an audiologist. I got charged $50 which isn't too bad considering it's right in the middle of NYC where everything is expensive. Of course a couple weeks after I got my customs in the mail I found out about a place that does it for $20 near my house..
If you can find a reasonable price from an audiologist ($100 is not) I would go with an audiologist but of course you may be comfortable with saving a couple bucks and doing it yourself. I'm sure DIY isn't too difficult as when I got mine done at an audiologist it didn't look too complicated.
rawrster, could I get info on that audiologist? I've been debating on getting customs and knowing the name of some local audiologists would be great.