I taught Combatives & Self-Defense up to 2015, and made a technical study of boxing in 2010.
Boxing here is pretty much the cheapest MA/self-defense (then it was $65/month.)
However this new boxing gym I found is really inexpensive and excellent.
It’s a true non-profit started by a church (with no requirement to participate in the church to attend): $20/month
They have a giant room, with a full size pro ring, 2 exercise areas, a bag area with maybe a dozen bags, and a small free weight area and several coaches.
Very welcoming. They run classes Mon-Tue and free practice Wed-Thu.
I suppose the only complaint is not open Fri or Sat.
Nice people too; everyone is welcoming.
To be clear, most boxing students do NOT do “full contact” but rather limit it to medium or even light sparring where you work for good technique more than try to hit the other person really hard.
I found a young man who was repeatedly hitting the bag and asked him if he wanted to practice parries, then asked if he wanted help.
This gave me a way to motivate myself to keep going despite exhaustion, remind myself of technique, and I just love teaching someone who is interested.
We are VERY LIGHTLY sparring much of the time, not ever hitting with force.
(I am a Systema teacher too, so I hit like a freight train – and teach this – and would never hit a young man like that full force.)
Like a lot of people, he was dropping his fist or “re-cocking” in an effort to hit harder.
One secret of hitting is to throw from wherever your hand it at the moment.
This is also the reason you always return you hand to the starting position after a punch (unless there is a positive reason to do otherwise.)
Tried to show him how to “move the tool to the target” with movement of the feet but pretty sure he didn’t get that – by that time I was very tired and with my mouth piece probably not intelligible 
