This probably just me preaching to the choir, but before you enroll your son in a school that may not be optimal, take the time to visit the school, meet the principal, and meet the teachers. Learn the full area that the school draws from and consider the neighborhoods. I had the pleasure of being bused into a school that was awful as a child. Awful. Fights, low standards, weapons, gang related families, etc.
No amount of parenting and support at home will make up for that.
If you have any concerns about the environment your 5yo will be entering and spending most of his day, pay the money and move.