Other costs, apart from the spread, you need to take into account when dealing in CFDs are the daily financing charges. Financing charges represent the cost of borrowing the capital that is needed in order to open a position. CFDs positions that remain open over-night are subject to those charges, incurred on daily basis.
A long position attracts the financing charges, as effectively, by depositing initial margin, you borrow capital from us to cover the rest of it (i.e. the difference between the initial margin and the total value). For short position, on the other hand, financing interest may be credited to your account, as the opposite applies, meaning, you lend capital to us.
It is worth noting that those charges do not apply for any CFDs with an expiry date (such as for example CFDs on Futures) as the price in the underlying takes that already into account.