Blocktrades' fees go down as you trade more. Put in the figure for 1 SBD, then 10, then 100, and you'll see. For BTC, most of the fee actually comes from the BTC end, and would apply in most exchanges.

I do find them reasonable, if you trade at least 10 or so SBD, though with SBD's current prices, it might require a bit more.

Edit: Also, it depends on the coin. I checked just now for instance, 67 SBD can lead to $122 worth of BTC, but $125 worth of Ethereum, while the nominal value is $129.31.