i have worked in orthodontics for 40 + years. I don't know of any one who avoided the full braces by doing something ahead of time.
I would get a second opinion. I think the price is too high.
In my office we often do an appliance of some sort on little kids if we need to widen the upper palate, but we always tell the parents that this is stage #1 and the child will need braces when the other teeth erupt. Your total bill should not be over 5 thousand, including any early intervention treatment.
I would ask if this will be likely to improve things enough to prevent future treatment, and , if not, would it make any difference to wait a year or two.
You know your child best and if you feel he is too young for this I would recommend waiting until maybe next summer. On the otehr hand, boys tend to become less co-operative when they reach their teen years, so I wouldn't wait too long. If the child has a disfiguring orthodontic problem, getting it fixed can make a big difference in his self esteem and in the way other kids treat him.
My son had a huge overbite and the kids made fun of him, so I had his braces placed pretty young. I think he was 10. By the time he got them off he was 12 and refused to wear his retainer, but so far his teeth have not relapsed, so I guess he is just one of the lucky ones.
Bottom line is I would get a second opinion before committing such a large sum of money to a partial solution.