This is the correct answer. I volunteer at a local place repairing their donated bikes and have gone through this exact bike in similar rusty condition. It's not worth it even when you've got the spare parts on hand at zero cost.

If you're determined to rebuild it the best option is buy another used MTB and move the parts over. But at that point hopefully it makes sense to throw out the Huffy. Maybe save the tires, grips and seat if they are useable.