I have a junior in honors engineering at Purdue. Out of state COA without any merit will still come in around your $40K budget. I think he will be accepted to Purdue with his stats. Honors college is where it is more hit or miss but IMO, that shouldn’t be a deal breaker. There are plenty of other living/learning programs that mimic some of the benefits of honors college at Purdue: Learning Communities - Learning Communities Available to Students in the College of Engineering
UMD CP would be another school with a great engineering program that would come in at budget.
If your son would like to add a private to the list, he should see enough merit at RPI for it to come in around $40K too.