I do feel for you, $1000 is a lot of money to come up with, but even a regular vet dental bill can come to that price if there are extractions or unexpected extras . But 107B is right, X-rays reveal what is hidden below the gumline and that is very important. I pray that this one time you will be able to raise the funds to do the required dental work, and after that she may be fine for a long time.
I get the problem with teeth cleaning at home. I have tried every brush and method to effectively clean my boy's teeth but cannot get near the back ones that tend to get tartar. I do the best I can but no way could I do a good enough job to prevent regular dentals. Many of the issues with a YT's teeth are unfortunately genetic, and home cleaning cannot always overcome that. There are oral sprays and topicals that can help and you might give those a try. Once this dental is done you may find a vet who does non anesthetic cleaning, and that would be much less expensive.
In the meantime please just consider getting her teeth in good shape now and do your best to clean them as best you can, and worry about the next cleaning when it is needed
She may do well after this dental and need infrequent ones after that. Do not get too concerned about the future at this stage.
I hope the estimate comes out reasonably and that your baby gets all the work done soon.
Good luck and try not to worry about the procedure.
PS. I don't think you can be certain that she has no pain or discomfort, dogs are very good at hiding pain!