J.F.
I see your dilemma. Here are some other options to maybe consider:
*Look into charter schools in your area. They are USUALLY similar to style and size of a private school, but are FREE because they are public. They often have a waiting list, and use a lottery system. But, openings happen as the summer goes by.
*Look at hiring someone to drive and provide before/after school care for him at a much lower cost. Ask your old babysitter for a recommendation. I've also had luck with www.care.com if I can't find someone via word of mouth.
*Look at the Boys and Girls Club in your area. Ours is only $20 A YEAR for afterschool care until 6 p.m. They provide the snack and transportation from the school (using the school's bus). However, the limit HERE is 6 years of age.
*Look into being able to go to another public school in your area...although transportation is more of the issue??
Don't use your old babysitter's address. More than likely you will have to provide at least 2 utility bills in YOUR name with that address (as they do here). Do you want him to start, do well, and then they find out you aren't living there (and what are you teaching your son???)? They will either require you pay tuition and/or send him out.... mid year???
I've taught inner-city schools, medium socio-economic schools, and charter schools. The biggest difference is parent and teacher involvement, NOT money or resources. If you have the right teachers and administrators working with parents who value education, you have a winning team. Class size is the next biggest factor.
Good luck!!