Varies a lot. I've seen everything from 8,000yen-17,000yen. Strangely, Osaka shops don't seem to care about spine cards very much. Stores here tend to sell games for the same price if it has the spine or not. Meaning you can get a beautiful copy for a good price, or get a so-so one for the same depending on your luck.
DenDen Town used to be great. But it's shrunk over the years. ******* Super Potato has slowly been buying out the local shops to increase their overpriced monopoly. Still though, I prefer DenDen over Akiba, way less tourists
. Also has probably the best MSX shop in the entire country, if it's your thing.