It might help to realize that a cheap "mountain" bike isn't intended for-mountain bike riding, really. Although being 125 lbs will help a lot on that.
Most of us started at some point on a cheapo bike and after a while discovered why you shouldn't ride a cheapo bike.
Target might be a notch above Walmart, but if you buy a bike either place and actually ride it much, figure you'll be buying a better nicer one after a while, anyway. So it's not like you're stuck with what you buy now for 20 years or something.