NOTHING in common??? Come on now... I dont claim to be a firearms expert. Far from it. If I was I wouldnt be posting questions on this site. I know there are many differences. But these rifles have much in common. I just want to know if the differences justify the cost difference.
I don't want to seem trite, and having bought my first M1A and my first Mini-14 some four decades ago, I'm pretty well conversant in their qualities.
Here's why they have nothing in common, and why your question cannot be answered without additional context: They don't do the same JOB.
It's like asking if a 8 ounce hammer or a 16 ounce hammer is better. It all depends on if you want to make furniture, or frame houses. One is worthless in one place and the other is worthless in the other.
MISSION is always first.
CALIBER is picked to suit the mission.
PLATFORM is picked to shoot the ammunition.
If your mission is to go to the range and go BANG BANG BANG and then grin, then you will be happy with either.
If your mission is to carry it stuck behind the seat of a pickup truck on the ranch to deal with Coyotes, then the 5.56 is fine, and the Mini-14 would be a good choice in the 5.56.
If your mission is to defend your ranch against "xxx" and they are likely to be hiding behind the 20 inch trees that are 200 yards away and that you don't want to cut down, then the 7.62 is the ticket, and the M1A is a good platform for that.
So choose your mission.
The M1A is a higher quality weapon when it comes to mechanical construction and overall quality. It is, essentially, MILSPEC. They can be tuned into very fine match quality/sniper quality rifles.
The Mini-14 is a die-cast receiver rifle, of adequate quality, and a very good value for the money. Those are not "glowing" endorsements, but for a civil user the quality is fine. It is not likely that it would be tunable to become a precision match quality/sniper quality rifle.
Really, other than cosmetics, they have nothing in common.
You need both...