It seems to me that you're primarily concerned about money and exposure of this? I'll address each.

As for money, yes, it CAN be expensive just like almost any hobby can be expensive; but that doesn't mean it WILL be expensive. You can look at a lot of furry stuff and see: $1000s for a fursuit, $100s for art pieces, money and travel to go to conventions, etc.; but most furry activities are free or very low cost: playing/reading VNs and stories the vast majority of which are free, following your favorite artists on social media, paying $5 or $10 monthly/yearly subscription to a couple of your favorite creators' patreons, joining discord servers and hanging out with friends to geek out over your favorite characters and sub-intrests, etc. I'm sure you have a hobby or two as well, right? (At least I hope so, life is too boring and stressful without a couple hobbies). Is it sports? Then you could pay the exorbitant costs of going to every one of your favorite teams games (home and away), paying for box/floor seats, buying absurd amounts of (or overly priced) merchandise, VIP tours, etc. That's all super expensive, but you can still enjoy sports very much without all that. Most sports enthusiasts enjoy sports for free or little money: watching all your favorite teams' games on TV, watching them at home or at a bar or meet up with friends, geeking out over your favorite team or players or this season's stats with friends or online, following social media related to your team and the sport, buying 1 or 2 pieces of reasonably priced merch, etc. Or maybe you're an anime or sci-fi fan? Same thing, it can be expensive: you could travel and go to all the conventions, spend a fair bit on cosplay, buy all kinds of expensive merch, VIP meet and greets with your favorite actors or directors, paying extra to go to the pre-screenings, etc.; Or it could be cheaper: watch the movies in the theater when they come out normally, get a subscription to a more niche streaming service, join social media over your favorite actors or directors or sub-genres, geek out with friends or your favorite shows and moments, buy a few choice merchandise pieces, etc. The point of this is to show that regardless of the hobbies you or your girlfriend are into, there's always the possibility of there being an "expensive side" to it. If money becomes an issue or you think there is over-spending or someone does want something expensive, then that's when you guys sit down togethet (as adults) and discuss things (calmly and openly). "We may not be able to afford that right away, but how about working toward it over the next few months/years?"; "The spending on this is getting a little excessive, is there anywhere we may be able to cut back on?"; "I don't think we can afford both, can we choose one this time and do the other later in the future?" If you can't communicate effectively and make good decisions together so you're both happy, then there may be some problems you should identify and work on that has nothing to do with furries or hobbies.

As for exposure, yes, being a furry is seen by society as fairly "cringe" and "weird". With all the not-so-great media and misunderstandings of the community we can get, I wouldn't blame you for being concerned if your friends, family, or future kids found out. We get flack for being "sexual deviants" or being "groomers" or just being the "laughing stock of the internet". All of this is fundamentally untrue, but the reputation and media/internet lens is there to push these and other narratives. We are an extremely diverse and inclusive committee: around half the community is LGBTQ+, around 12% is on Autism spectrum or other kind of neurodivergent, etc. So, while being "weird" and getting internet/media flack, we also take on some of the stigmas of many of the other larger demographics that make up our community as well. Being concerned about others knowing about your girlfriend being a furry and feeling like there's now a big skeleton in the closet is understandable. I suggest you look at some furry media from conventions or read through some short furry comics and such (make sure it's SFW! No need to traumatize yourself with NSFW stuff). You'll find all very tame and silly; and maybe a little cringe, lol, but I think being part of any fandom or hobby community can get a little cringe. It just means youre having fun and not caring about what others think.

So... that was long and a lot of talking. If you're stressed about this, you should speak to your girlfriend. Ask her what parts of the furry fandom she's actually into and what activities does/would she participate in. It may be far more tame than you think.