Really the research needs to be done on what nutrients dogs need and what food contains them - the cheap foods will all contain fillers that the dogs do not digest but just poo out.
Dogs have survived as scavangers and will survive on rubbish food but personally I do attempt to give them the nutrients they need. This does not need to cost much money.
Cheap food has ingredients added to them that encourage the dog to eat. Kibble has palatability enhancers which make the dog want to eat it. A bit like giving a sprout to a child or a jelly baby. The child will love the jelly baby but not the healthier sprout. So saying a dog prefers the cheaper food is not an indication of what is a healthy food. The enhancers are usually made from high fat high sugar content.
Cheap food has to be fed in larger quantities as it is full of food that can not be digested so in the long run can be more money and certainly will cause issues over time.
Cheap dog food is fast food and there are the health risks associated with using it long term. Cancer kills 46% of all dogs various studies have linked this to poor nutrition in dogs over their life time.
Cheaper dog food obviously contains cheaper ingredients and can legally include meat from dead, dying, diseased and disabled animals.
Corn in cheap dogs food can actually be corn dust that has not nutritional value at all.
The increase in kibble diets has also coincided with increase in dental decay in dogs as kibble does not clean the teeth but coats them which causes more decay.
Beet pulp for example is not digested by dogs just makes the poos huge and smelly so why give it to a dog.
Research nutrients rather than food and then work around that.
Expensive manufactured food may not be any better but usually has less fillers but there are cheap healthy easy ways to feed dogs.
I don't think we have to bankrupt ourselves to feed our dogs but I do think our dogs deserve that we fed them appropriate food for their needs