I’ll dispel one notion up front – other options available from the Singer store include foot-pedal sewing machines, no electric motor. They’re needed in this country with only 62% of the country having electricity, and those with electricity having frequent power outages (we’ve had more than a dozen in the last week, for example – but it has been particularly bad lately.) So yes, it is possible that when the description says motor optional, they do mean it can be foot-pedal operated.
I’ve lived here long enough that I’m used to these things and I forget that not everyone else knows what I know. 
Other brands are likely not available in this country, or if they are, I’d have to really hunt for them. Singer is a chain store, and in that sense, they’re already much more reliable than other stores that won’t honor returns for defective equipment and can’t do anything about warranty issues.
The button-hole function is, to me, useful even if I only use it occasionally or seldom.
So*. With the more expensive one listed as motor optional, combined with it being cast iron (translation, heavier than an anvil), it’s out.
Buttonhole function important = less expensive one out.
But. Will the mid-range one also have a zipper foot?
But what’s that two-needle thingie that?
Yeah, I’m pretty sure I’m going for the middle one. And if Fahim is willing to spend more money, why not get one with more features?
