In many, many ways.
- The cone itself is probably the main difference, and you could fit an NRP one in a chinese one, but you'll be up the price ladder a bit. It's the 'tonewood' of resonators, that bit of aluminium alloy, its gradients and lines...
- Most resonators come in concert size only, NRP makes them in others as well, including soprano format; same goes for the soundbox material, NRP offers a range of materials besides the standard brass (steel, 'german silver')
- The 'soundbox' affects the sound as well, being sturdy without buzzes, minimalizing the bounching around of the sound before it leaves the instrument are quite essential aspects, but the material of the soundbox also colours the sound.
- I agree, there is a bit of price that has gone into (A) being made in the US, (B) having a nicer design and style and (C) having a brand name that eases resale value. none of those affect the sound, but they do influence the price.
I've had a Johnson, a Beltona, a Dobro, an NRP, and I've played a Gold Tone, a Ron Philips, Kala, Gretsch and old National and probably a few more. Never tried a Argapa, alas. The expensive ones really are better, both from the sound they emit and from the playing comfort they offer.