You will need to register yourself £15 and your horse £15 for the CCI*.
If you want to compete abroad or do the CCI** you would also need an FEI passport.
SW123 - if you need an FEI passport (ie for overseas or ** in this country) then it is £172 for a cover or £206 for a full passport. If you existing passport is on the FEI accepted list then you only need the cover if not then you will need a full passport which requires a vet to complete the diagram etc which will also add to the cost.
Also it does take time as the passport is passed around (see BE site for details) so could take about a month (or you can pay an extra £68 to speed the process up !)