Academically the math and reading they are doing sound well ahead of typical second grade in public schools around here. Multiplication tables usually aren't until third grade in many systems, and fractions are third to fourth grade. Sixteen chapter books is a lot for one term, though I'm not sure what you mean by "coding."
Check whether the local public school system has a "gifted and talented" program or (another term for the same thing) "advanced academics" program. He may qualify for such a program and that could solve your money problem while also getting him a good and challenging education. Ask to talk directly to a GT or AA instructor, ask how kids who are not already in public school test to get into those programs, etc. Fiind out if the programs are "pull-out" (kids get some higher-level instruction once or a few times a week, but are in a "regular" base classroom most of the time for most subjects) or whether the system has "centers" where the kids are in classes that are all-GT instruction, all the time, in all subjects. It will be up to you to determine whether it's right for your son.
A good education is priceless, absolutely, but you must also think ahead to whether you'll be able to afford college for both kids if you spend everything before they hit college age. You and your husband should think about retirement for yourselves too. Once both kids are older, you may be able to work full-time to help if you and your husband both decide to stay with private schools.