Yeah there was a thread on this a will back - I wrote a really long and detailed answer, can't be arsed to do the whole thing again...
Here's the jist of it - Big smasher of a tune might sell 7000, something like Machete or Timewarp or summat - the producer gets about 10% to 15% of the price paid for it, the rest goes to the label, the design, cutting house, distributer, couple of unions, and then finally the retailer who you bough the record from....
Net profit for the producer assuming they are on a 10% deal would be just over 4 grand - not much considering this would be a big, big tune. You'd need to do at least 5 of them a year to even make a living wage - which lets face it, no producer can do more than 5 massive tunes a year, if that!
DJ'ing, now that's a different kettle of fish you can make £1000 an hour at that, even if you're just fairly well known - considering that you can do several gigs a night, particularly on the weekend, not to mention the weeknight stuff you can fit in too, you can make more in a night than you would from releasing a big tune...
No wonder most producers get out on the road and start gigging as soon as they get known eh!