Just how successful was Brock's dental practice?

Not to mention he's paying child support for at least two of his kids by Reba (I don't know if his child support for Cheyenne stopped once she married, even though she was still 17 years old and living with her mother. But he did seem to at least help with things Cheyenne needed, so even if he didn't pay child support outright, he was helping out there.)

I remember Brock telling Cheyenne in one episode that he went to dental school by day and worked nights, and I believe Reba was working as well, so they may have been paying for his school as they went. Then by the time he opened his practice, they didn't have any student loans hanging over their heads.

I also think Reba went back to work when either Jake started school full time, or when she realized her marriage was in trouble, so while Brock's income may have been the major source of support for the family, it wasn't the only source.

I also think that Brock and Reba, as a couple, weren't prone to overspending--there's jokes (even by Brock himself) that he's cheap, and there's no indication that Reba ever did do much unnecessary overspending. They'd spoken about their crappy apartment when they first married, and apparently the family lived in a smaller house before Jake was born. So it may be that by being smart with their finances, Brock and Reba had enough money saved up that when the marriage went sour, buying the condo wasn't a problem for him.

Though with his marriage to Barbara Jean, his finances might not be in such great shape......