PS-1 > HP-2i > HP-2 ~ PS-1000 in term of price
As for answering which one is better sounding... I have no idea
Some people bash the GS- and PS-1000 but love the PS-1 or the HP-1000... or the RS-1, some people just feel like the two bigger form factor Grados are a side-step rather than an evolution.
Still, some of die hard Grado lovers might use their their PS-1 interchangeably with their PS-1000, or even prefer that later one they see as the ultimate John Grado headphone. They swear by the "Grado sound", and though they might have a HP-1000 somewhere in their house, they may be indifferent about it, or might have sold it a while ago already.
On the other side of the medal, many Joseph Grado HP-1000 owners on Head-Fi think of it as the best Grado, and some use it as their main horse or as their "one" and only headphone (I've spotted about 10-15 people like that on Head-Fi, with one preferring it over the Qualia 010, and one the MDR-R10, etc.). Also, some people who don't like nowadays Grado sound like the HP-1000.
It's up to you to collect information, make yourself an opinion, or judge with your ears by trying it at a meet. They're not that uncommon in the US (at least the HP-1000 and the PS-1000
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For me it's the HP-1000, yeah, but many John Grados aren't behind it by much at all; I love my SR325i with flats, my vintage RS-1, and now I can't wait to receive my full Magnum v2.5 (drivers, but refurbished with v4 metal parts), which also sounds like a Grado, but more refined and "less harsh" apparently.