Homeschooler and former academic expat here. I see two questions here: (1) Should you homeschool? and (2) Assuming you should, how can you manage that happily?
(1) No education is perfect. What are the pros and cons of the school vs homeschooling? Are you happy with your son's school, except for the cost? (It's not clear to me whether you'd rather instruct him yourselves compared to school or compared to homeschooling with tutors etc.) If so, I would look in to ways to keep him there. Maybe you could pay the tuition in instalments, or maybe a friend or relative could lend it to you to be paid back over the course of the year, maybe this would be one thing worth going into debt for (presumably only temporarily), etc. Or maybe the school is not ideal anyway, and the tuition just tips the cost/benefit analysis definitely over to homeschooling.
(2) Assuming you do want to homeschool (which can be very fruitful for kids on the spectrum--as you say, you know what he needs), you're right that there are potential pitfalls, but these can be avoided or minimized with some forethought. I think the key is to recognize that time, like money, is a limited resource, and homeschooling means adding another job to the ones you are already doing (though admittedly not a full-time job).
First off, that means your wife's concern about time for the two of you is really, really valid. You (plural) should make a plan that dedicates time for the two of you, and protect it fiercely.
You'll have to think about whether you can cut some other activities.
You can also think about ways to homeschool efficiently. Some examples: writing across the curriculum; incorporating tech ed (if you really need it) into other subjects by using tech tools for writing or data collection; combining foreign language and social studies by learning about your host country.
As to your son's adaptation to homeschooling, it should be possible to arrange the academics so those changes are beneficial for him. There are resources, including support groups, for homeschooling special needs kids. If your son has friends through school, you will have to make efforts to sustain those social interactions. If there's a DoD school near you, I hear that they are very accommodating to homeschoolers when it comes to things like extracurriculars, taking one class, etc. I don't have any personal experience with that, since our time abroad wasn't anywhere near a US military location.
Finally, you (personally) should acknowledge to your wife that you've flipped positions since five years ago, so it's understandable that she's peeved. I would be honest about what has made you change your mind.
Good luck however you decide!