Re-grading a Part-FCL PPL to a LAPL isn't an initial issue and shouldn't cost the figure you quote.
Their stupidly confusing scheme of charges doesn't specifically include 'Re-grade of Part-FCL PPL to LAPL', but on the website they quote £40 for 'Conversion from UK issued JAR licence to a LAPL', so I cannot see it costing any more for re-grade of a Part-FCL PPL to a LAPL....