The cheapest way to send a deposit such as this is in euro notes using the Airsure service : International (Signed For).

This service is available through your local post office. The envelope containing the money must be signed for by the recipient and, in case of loss, its contents are insured for up to £500. For an extra 40p, you will also be informed that the letter has been delivered.

Sending a payment electronically from your bank account to that of the gite owner would cost more. The Royal Bank of Scotland, for example, says it would charge a flat rate of £9.50 for such a transfer.