You beat me to it BDGA!! I was just about to say pretty much the same thing. You forgot to mention the advertising work he has done (Outburst, Atomic Kitten's Greatest Hits, Walls Ice Cream, etc etc ... )
I think having your own show, no matter what time it's on, would pay pretty well somehow! Especially as it was the highest rated night-time show on ITV in 2003. I don't think Kate's little stint on Ri:se can compare to the amount of work that Brian has done, although I wish her well. Success isn't just about money either - it's about being respected. Judging by the amount of work Brian gets within the industry which isn't necessarily televised, I would say he's pretty well respected, and is gaining more and more experience all the time.
Just because he didn't sell his soul to the tabloids doesn't mean he hasn't made himself a very respectable amount of money. We will never know for sure, however, as he is never likely to spill his guts (literally!) in the same way as Jade.
Good luck to all of them - I hope they all manage to make a decent living out it all.