I don't know what dentistry costs in your area, but I do want to ask you if your children are drinking fluordinated water. If they aren't you really need to get them supplements. No matter how careful you are with their teeth, if there is no fluoride in their water, they'll get cavity after cavity after cavity...
You need to find different dentists. This one is just too expensive and too eager to sedate small children. See if you can find a Children's Hospital dentist who owns his or her own practice. That's what I used to do with my kids. This man loved children and worked at the hospital, and had his own private practice. He used laughing gas (not sedation) for children which my own children had with teeth extraction and fillings. The cost of laughing gas is a fraction of the cost of sedation.
When we were kids, we had teeth filled and pulled WITHOUT being put under. Parents had expectations of their children and worked through all this with them. Parents and dentists talked together, dentists were kind to children and didn't strap them down and work on them while they screamed, and children got the work done. When you have ped dentists who don't want the "work" of calming children, some resort to putting kids under, strapping them, not working with parents. You don't have to fall for that.
Tell your children that they have to get their teeth fixed so that their mouths won't hurt. Do NOT let them fuss in the dentist chair. Tell them in no uncertain terms that they WILL behave. I made it perfectly clear to my kids that if they didn't cooperate with the dentist, that they would lose a beloved privilege. I also told them that if they were good for the dentist, we'd go to their favorite toy store afterwards. Carrot and stick approach...
At home I prepped my kids and showed them the laughing gas mask they would wear, and they practiced putting it on so that they wouldn't get scared of the mask. My younger son fell asleep while his two front teeth were being pulled. My older son was very apprehensive (his personality), but it was enough medicine for him to get through the procedures. This is much more safe than putting them under with sedation, and cheaper too.
Keep researching. You don't have to pay $6000 for fillings.