is there any reason all the prestige S models are about 400 dollars more expensive than the prestige RGs?

just checking on musicians friend a brand new RG2550Z is $900 while a new S2170 is $1300. do the mahogany vs basswood make such a huge difference in cost?
the S series is nicer maybe? just a thought.
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I'm not sure if those are actually equivalent guitars, so it is hard to say. If I remember correctly, there is actually a point where the regular RG and RG Prestige lines have a price overlap.

The S series has different options, different tremolos, almost positive different builders, and uses a different wood, and all of those will effect the price. I think some of the S Prestige use some pretty expensive woods for the tops as well.
They don't relate
The prestige S's are REALLY nice, like the best woods and top of the freaking line construction, where as the RG prestiges have a much wider price bracket from the 1570 per se up to the through neck beast that resides at the top of the pile

They're not really comparable directly, although the normal S's are actually very good (470 for example)
IMO the S's and RG's arent on the same playing field... the base model S is a definate big step up from the base RG's. Matter of fact, I would take an S470 over a RG prestige anyday, mostly because I feel like most of each are fairly similar (I've heard both have weak stock pickups and great necks and trems) but I like how the S470 hugs your body, plus I generally dont like pickguards on normal shaped guitars. I guess over all, RG's just arent my cup of tea. Once you get into that price range though, just about any guitar (Ibanez anyway) will be a pretty good guitar.
Fingers -> Schecter Damien FR -> Fulltone OCD -> ABY Box -> Bugera V22 / Peavey 6505+