Please don't buy a "bargain" Rottweiler.
"You get what you pay for" doesn't even begin to cover it.
In this breed, the "cheap" puppies are just about guaranteed to come with a host of expensive, painful, and sometimes ultimately fatal genetic health problems. (Did I mention "expensive?") That's if you are lucky. You can also hit the jackpot and get an outrageously vigorous one who takes over your household by use of his teeth, has strange obsessive-compulsive behavior (light chasing, pacing), aggressive "fits," eats other dogs, etc.
$1000 is not an unreasonable price to pay for a Rottweiler puppy from healthy, genetically sound, sane parents, with a contract from an ethical breeder that includes a genetic health guarantee. A pup from parents with higher-level working titles will be more. Any Rottweiler pup should come from parents with OFA clear hips and elbows, or PennHIP in the top 50%ile, cardiac clear, normal thyroid, CERF. They should be free of IBD, never have "bloated" (experienced GVD), and come from bloodlines that are relatively free of osteosarcoma. The pups need to be aggressively vaccinated against parvovirus, to which they are famously susceptible. (I am not an advocate of aggressive vaccination in general, but it's common for whole litters of Rottweilers to be wiped out by this disease in a blink.) They must be socialized early and often, with everything and everyone, everywhere, starting at the breeder's and continuing under your care.
Of course, just because a dog is expensive doesn't mean that it's a good dog, or healthy -- there are shysters everywhere, and good breeders can have bad luck from time to time -- but you are really taking your chances trying to go cheap. Especially since you have children. A well-bred, mentally sound Rottweiler is a great dog to have with kids. A backyard-bred example -- I wouldn't let one near my nieces on a dare.
In 17 years as a dog trainer, I've only flat-out told clients to put down a dog twice. The first was a sociopathic golden retriever that had a bite record in the double digits, seizures, and a master plan to eat every kid in the neighborhood, which plan his owners were bent on enabling. The second was a three month-old Rottweiler puppy that came up the leash and attempted to seriously attack me in a sustained and committed manner when I mildly annoyed him. The owner's young kids were already terrified of the beast, and they were right. They'd bought him cheap from a local "breeder." Didn't see the parents, which were locked in the barn -- but did see the barn siding bulge out as the sire attempted to break through the wall to eat them. That would be your sign, you know? The pup was not right, and nothing was going to make him right. The owners spent thousands of dollars on multiple trainers (none would give them answer they wanted to hear) and vets (ditto) before doing what had to be done. It's a miracle that their son was not mauled before they did; that's what happened to the son of the golden retriever owners.
"Cheap healthy purebred dog" is just about an oxymoron.
If cheap is non-negotiable, get a good adult mutt.
If it must be a purebred Rottweiler, spend the time researching breeders, and be prepared to spend something for a pup that a knowledgeable person actually put some care and thought into bringing into the world.