I know it needs a 6-month/50 hr check and an annual. I have been told that the 50 hr check should cost £350 and the annual around £2,500.
Maybe you're in the South-East, but that looks incredibly steep to me. Down here in the South-West a star annual (for CofA renewal every three years and a much bigger job than an annual) costs £12-1500, supposing nothing major is wrong. £350 looks outrageous for a 50-hour check, given the very little it involves. You can do it yourself anyway.
QDM