Another thing I'd add is I don't use any kind of 'buds' (besides what goes in my bong!), but I do get custom-molds instead of using the generic domes; only cost about $60 more and well worth it.
@mahler123 - not all Costcos are the same, as you've found out. Fortunately the one I go to has an audiologist who's been practicing for a few decades, and they've got all the lines and models that are on their website. Looks like your Costco has a dodgy hearing-aids department; if they're not carrying certain lines they should be, you might want to let Costco management know about it.