I know a lot of people on this board do the student rush or lottery tickets--I'm too old for the student rush, but I think you can get tickets for around $20-$25 that way, depending on the show.
I almost never pay full price for a ticket. I usually either look for discount codes via Broadwaybox.com or Playbill.com, or I go to the TKTS booth. Tickets bought this way still aren't cheap--I'd say they average about $60 each--but it's a little better than full-price.
I think if seeing shows is really important to you, you make room in your budget for it as best you can. I'm willing to scrimp on other things (eating out, Starbucks, clothes, etc.) because seeing Broadway shows is one of the things that gives me the most pleasure in life. Other people (like my husband) don't really understand this. If they see a show once a year, or even less often, they're fine with that (that's why I'm glad my 15-year-old son loves theater and is happy to go along with me!)
Of course, if you're on a really tight budget, and already have almost no discretionary income, then yes, even a $20 or $25 ticket is going to be difficult. I'm just saying that I don't think most people on this board are seeing shows multiple times at $100 a pop.
Maggie-the-schnoodle