Cost is often something that scares people away from classical concerts. The “brand” for lack of a better word, seems pretty tony, and people automatically assume that tickets for live performances will be out of reach.
Although some tickets for famous performers at big venues are indeed pricy (although not necessarily more so than those of other live events), there are lots of ways to hear classical music less expensively. Here are a few I use, and I’m sure there are others.

Reduced-cost “day of” tickets. Many classical organizations have rush or discount tickets and if you can spare the time to get to the venue early, you may get a very good seat for less than a movie ticket. I attended a lot of Boston Symphony Orchestra concerts this way. Check the web sites for the policies (often called “rush tickets” and sometimes limited to students).
Meet-Up and Online Newsletters In DC, there is a very active classical music Meet-Up, which frequently has offers for discounted tickets. Through that resource, I found out about a Kennedy Center mailing list you can join for notice of last minute deals for unsold tickets and sometimes deep discounts on advance sales. Look for these kinds of resources in your areas: in addition to Meet-Ups, these sort of resources can be associated with a venue, an individual company, or a presenter. Of course, they want your email in return and the right to market to you, but if it’s relevant info, it’s a perhaps a reasonable trade.
Ushering/volunteering This is not particularly my thing, as I’m fairly promiscuous in my musical tastes and don’t want to spend say every Thursday at the symphony. But people I know have found it a practical way to hear a lot of good music (or see theater for that matter).
Trusting to luck Just showing up an hour early at a hall and seeing if somebody has a ticket to give away is a risky practice. I would not recommend it for a concert you have your heart set on. But it has worked for me. Ticket resale is sort of a murky practice at many venues, but giving away an extra is kosher, so some people prefer to do that, even for sold out shows.
Conservatories and Music Departments’ OfferingsIf there are musical education organizations in your community, check out their free concerts. Elite outfits, like Indiana University and its world class opera program, or the amazing string faculty at New England Conservatory give performances that are deeply satisfying experiences. But even if you aren’t lucky enough to be near programs like those, it’s likely that there will be music worth hearing in your community, be it at a school, a religious or community organization, or another non-profit. They will be happy to have you: musicians want to perform!
Roll your own I have turned from a critic to a participant over the years, and now play chamber music with friends and sing in amateur ensembles more often than attending concert. Opportunities abound and they are rewarding in themselves, and also frequently lead to chances to hear other concerts. Even if you are not a musician yourself, informal house concertsare cropping up all over, and these can be nice ways to experience music.
With all the money you save going to free or low cost shows, you can consider funding that once-in-a-lifetime concert going experience. Most music lovers have a “dream list.” A friend of mine wants to go the New Year’s in Vienna concert at the Musikverein. I’m content with watching that one on TV, but if you know a cheap way to get to La Scala, Bayreuth, Teatro Colón, or the Berliner Philharmoniker, let me know!