My hairdresser uses it in the salon and I bought a bottle from her for £10 - the price seems to vary enormously online. She says it can be also used as a setting lotion, to boost curls between washes, and, apart from shampoo, is the only hair product she takes on holiday.
250ml is a big bottle so I would imagine it will last me ages - have been trying it for the past 6 weeks and it has transformed my hair!