Lost: A yeshiva with a staff for secular studies is twice the budget, or the MO dayschool model.
Your following description is similar to what I see in MO model. It is (also) not sustainable. Both parents exhausted working full time to pay for schools, kids seeing this are not so excited, and all other problems given that not all kids are observant in school …
As to the cost of general studies in schools, I think it can be gradually improved at limited cost, provided there is a will and recognition of the problem. Use computer-based classes, focus on those kids whose parents want to give them extra general studies, obtain government funds for general studies.