Hi Joshua, and welcome to FISD.
Unfortunately the Honorary membership program is for the actors, producers, directors and others involved in the movies and TV series of Star Wars and not everyday members.
The only way to join the 501st is through your local garrison, first as a cadet, as the only limitation is members must be 18 years of age and up. You are a cadet until you can build a costume that meets the requirements of the CRL and become fully approved.
This gives you the opportunity to learn how to wrangle (be the eyes and ears of those in costume) yeah visibility is limited and some costumes can be restrictive in movement and uncomfortable.
Many do join and start with a less expensive costume like an Imperial officer costume. Still not without reasonable cost, but it is cheaper than a full accurate First order or even original trilogy Stormtrooper outfit.
The 501st is the definitive Star Wars costuming group, and with that comes a reasonably high standard in costume detail. It is why we are known as the best, and why Disney Lucas Film call on our members to represent them at events and even star as extras in film and TV shows.
It's the fine details we take pride in and why Halloween style costumes don't make the grade.
I wish you well in your journey joining the 501st, it isn't a cheap hobby in general, but you have some more affordable options through different costume choices.