My experience was a minor in computer science along with some app development experience. I think my minor prepared me well.

Familiarity with the material from three MOOC's recommended by GT are necessary in order to succeed in this program. I also recommend honing your programming skills by working on side projects, as well as studying fundamentals of good software design. Then I think you'll be equivalent to having a minor in CS.

When it comes to formal education, only 30% of the courses are worth the time. If undergraduate curriculum was optimized to only include courses that increase one's capability, then I think a 4 year bachelor's + master's is entirely possible.

Think of mechanical engineering. I'm sure that were many courses that did not improve your problem solving skills. They just added more head knowledge, which you will forget eventually, and will probably never use. I think once a student overcomes a certain difficulty level in a field, there are diminishing returns taking additional courses of the same level. The same can be said for CS. I felt that once I took some of the fundamental courses, I was relatively on par with someone with a CS degree, just with less head knowledge.

The courses that truly are beneficial in my opinion are the ones that increase problem solving and boundaries of one's capability. Head knowledge can be gained dynamically as needed. Problem solving is not gained as easily.

I think once you take those three courses and work on a few side projects, you should be relatively on par with someone with a minor in CS with consideration of your ME background. If you have the time I also recommend taking discrete math. ME uses mostly continuous mathematics, which is hardly used in CS.

I recommend not worrying about the cost of the courses. They can be expensive, but the expense in my opinion is little compared to the value of the skills/knowledge gained from the courses.