It all depend on the quality and accreditation which comes with the course. There are unaccredited manual handling trainers courses at low cost but with no standards and no accreditation, the certification would not be recognised by any UK awarding body. The best option is to do an accredited manual handling trainer course from one of the UK awarding bodies. Abertay for example provide a 2 day manual handling train the trainer course at £375 + vat but there are many companies who offer manual handling instructor courses that can be anything up to £700 + vat.
Best practice is to search for a trainer course that is recognised by one of the UK awarding bodies, then you will be assured that the manual handling trainers course has been fully quality assured and assessed for content.