Generally most retail products have around a 200-300% markup for profit, so I guess you would have to figure out what an iphone cost to produce right now, then compare it US wages, and you should have the answer.
I dont think it would be much more, as shipping from that far adds tremendous cost. If made in the US, it wouldnt need to spend weeks on an ocean going cargo ship. Plus the more people working in these US factories making these things, would mean MUCH more tax revenue, more people with more money in their pockets in the US.
Products I have had experience with in my jobs over the years boils down to this…
When I was in the pizza business, it cost us about $1.50 to produce one large pizza with one topping, that includes materials and labor, electric, rent, everything, and the pizza was sold for around $15. retail.
In my job now, I deal with convenience store type products, cigarettes, chips, sodas, point of sale items, etc. a pack of brand name cigarettes in KY costs about $.75 to produce (labor, materials, advertising, taxes, etc) and they are sold for around $6. retail.