I own a gym, 12000sq ft.. fixing to expand to 15000sq ft.
Lease is less than 10K/month with electricity.. We have 24hrs/LA fitness/Lifetime within 10miles of us, approx 1500 members.
You see what people don't understand is the memberbase simply pays the bills and allows for extra money to upgrade equipment and maintain the club.. The smart clubs know the money is made off of the members while they are there:
Personal Training - big one!
Smoothies - guaranteed to turn atleast 5-10/month off each active member on average.
Supplements - ditto
Pro-shop clothing - extra income, they pay you to advertise

Tanning - perk to membership and walk-in's pay per tan
Prepackaged meals - something 24hr and bigger chains don't offer, extra income/month
So add these things up and you can make quite a bit, keep your club up to date, very personable, clean, friendly staff and cheaper start-up and monthly fees than surrounding gyms. Many people don't like the big commercial gym atmosphere, therefore we really don't compete with those big guys, we have plenty more to offer that they don't and vice-versa, obviously you'd want to open up in a growing area or where you have a large population that either lives or works in the area.. Did I mention Personal training is the major income?

Ex: 5 in-house trainers that train 30sessions/wk. Club makes 25$ off each session.
150 x $25 = 3750/wk. Avg. $15000/month
Oh yea almost forgot, there isn't any money in a gym what was I thinking.