The UK postage comes to £8 thus:
Regular 1st class post of £1.27 (100g+)
Mail Lite Gold jiffy bag: 25p
Royal Mail Special Delivery: £6.45-£7.25 dependent on how much packing I use to protect the CD.
Grand total: (minimum) £7.97 or (maximum) £8.77.
I'd say that £8 is a fair aggregate. Obviously sending outside the UK using insured post is more expensive than this.