first off, you're comparing a relatively generic brand (Ritek) with a name brand (Verbatim). i just bought a Verbatim DVD-RW at a local computer store here in the states, and it was $16.99. while it is still cheaper in than $24.80, it's really close.
i guess it all comes down to manufacturers. maybe they put different list prices for different countries. at the same computer store where i got that DVD-RW, they also had TDK and Pioneer DVD-RW's, but they were both $24.99. so why are Verbatim's cheaper? i don't know, they're all very reputable brands.
have you tried ordering DVD-RW's from the states? if you can find a retailer who will ship to you, then you can get some pretty good deals.
tr