50 students and a kids program? Unless you have a couple hundred kids your BJJ instructor is probably the owner and he isn't making a killing.
The owner of my school has about 250 students, teaches four nights a week minimum and still has a full time job during the day.
Believe me he's doing it for love of the sport not for the paycheck.
Here is what i find hard to believe. Most people pay about $130/mo for BJJ classes.
250 x $130 = $32,500/month. Lets be safe and just assume this particularly gym averages only $100/mo per person and call it $25,000.
Most BJJ gyms are in studios, often in business parks. I doubt the rent exceeds $3,000/month.
A gym needs a phone line and a computer plus lights. Add another $250/mo.
He's also going to need insurance, and I have no idea how much that would be. Lets just call it $1,000/month (probably very high).
He'd also need to very rarely purchase mats. Mats to cover an entire gym will probably run $10,000-$15,000, and lets just say he is paying those off in monthly installments of $300/mo.
Total expenditures are probably less than $5,000/month, and total income is probably around $25,000/mo. That's $20,000/mo left over
without including retail sales and privates.
Maybe, I'm missing something, but IMO it would appear that an instructor with 250 students would be doing very well for himself, even if he employed someone an assistant instructor and/or office staff member him at a decent salary.
IMHO a BJJ business owner with a legit gym has every right to earn a good living, and I Hope they do. They put a lot into their training, took a major risk starting a business, and they work hard and work generally unpleasant hours (IMO). I just don't see why anybody with 250 students would ever "need" to hold a full time job in addition to their BJJ school.