bunbun was a breeder before i got her, but when i asked several vets about spaying and the cost, most of them suggested just letting fluffy have a litter or two also, that it greatly reduces the risk of cancers and reproductive diseases, and would "cost so much less and be less stressful" on the rabbit to do what nature intended.. .
One of my colleagues at work had a pet rabbit a few years ago and was told the same thing by her vet. They wanted to get a friend for their bun and their vet said to let her have a litter and keep one of the babies rather than spay and get a husbun for her. They borrowed a buck from someone and the 'extra' kits went to a local pet shop to be sold.
Had I not found places such as RU, I would probably have thought this was the accepted thing to do and may have done the same.