I struggle to believe that if your dog had a little of about 5 puppies you wouldn't need to charge much more than about £500 to still make some money
On the whole, I agree, but it depends on a lot of factors.
If you health test and take care to put your bitch to the best stud dog (by that I don't mean the one who wins the most prizes - I mean the one whose good points are likely to overcome her bad ones, health and conformation-wise) then you may have to go to the opposite and of ythe country to find her a mate.
If you have a brachycephalic (flat-faced), large headed breed (e.g. modern-day bulldogs, pugs, then you could well need a c-section for your bitch (a result of the rubbish KC standards that many breeders adhere to) that costs £££s - and often these breeds only have small litters, so there might only be three or four pups. £500 each will leave you well out of pocket.
A neighbour (who has now thankfully moved) used to breed labradors (she had SEVEN in an ordinary semi - great, fat lumbering show-type dogs). She had at least one litter a year - ALWAYS had problems with whelping (which is unusual in labs, and suggests she shouldn't have been breeding from those bitches), almost always had puppies with cleft palates in the litters (ditto) but continued to breed them because she "loved" her dogs, and they did well at shows.
She got between £800 and £1,000 for her puppies, (and this was 10- 15 years ago), but didn't often have more than five or so "good" (i.e. healthy) pups in a litter.