Seems to me looking at the rules, that rarity only comes into play on how hard it is to find the item. Has nothing to do with cost unless your are trying to sell it.
Using table 5-2, If I was on the outer rim, lets say Tatooine (R+2) a heavy blaster rifle (R6) would cost the same compared to if I was buying it on a Primary core world, like Corellia (-2), But if i BOUGHT it on Corellia, and went to someplace like Tatooine, if i found a buyer, I could sell it for up to 4 times its worth (Table 5-3).
Shouldn't the reverse be true?