That’s really not the case at all – the subsidies for high-end, mid-range, and low-end phones can vary quite substantially. The only real constant is the final subsidized price, which has settled into the pattern where, excepting sales or other specials, subsidized low-end phones are free, mid-range (or previously high-end) phones are $100, recent high-end phones are $200, and giant-screened phone-tablet hybrids (oh how I loathe the term “phablet”) are $300. And when there are deviations from those prices, they’re almost exclusively downward in the case of OEMs or platforms trying to gain traction (e.g. WP8 phones).
For example, go to AT&T’s website and look at the prices of the iPhone 5, Galaxy S4, HTC One, and LG Optimus G Pro. The subsidized price for each are all $200, but the unsubsidized prices are $650, $640, $600, and $550, respectively.
The vast majority of the people in the US market (where the “made in America” factor has appeal) will be buying it with carrier subsidy, which means it’ll be the same $149 or $199 that every other high-end smartphone costs regardless of how much more or less it costs Moto to build it here.
That Motorola is building a new phone is complete non-news – what everyone actually wants to know is what influence Google has on it and what customization if any they make to AOSP Android, and on that front we still don’t know anything.
That it’s being built in the US is kinda nice though, I guess? It could have some effect on the price of the device, but in the US market that’s pretty much irrelevant anyway.