I think there is a fair bit of speculation in the price. Short term factors aside, outlook for sugar must be good (deamnd / supply imabalance, competing land uses, ethanol).
I saw somewhere this stat: In a pure market, sugar cane would be the only viable biofuel with a cost of $35 a barrel (oil equivalent). The others are sugar beet ($103), corn ($81), wheat ($145), rapeseed ($209), soybean ($232), cellulose ($305).