Z-Cube charges approximately £10 shipping for 10 cubes to the UK. The cubes cost £0.51 if you order over 6
Cubezz charges nothing for delivery. The cubes cost £1.88
Z-Cube - £15 for 10 cubes
Cubezz - £18.80 for 10 cubes.
If you order over ten, I reckon eventually Cubezz will be cheaper, but for a reasonable amount like 10, go for Z-Cube.
These are the two cheapest shops, so COMPARE PRICES PEOPLE!