Re: £450 or £850?
A kit with mesh heads is much closer to a "real" drum head. This is especially important for the snare because it's played so much more..
I would search for a used kit with mesh heads. The Roland stuff has been very good for me and I've picked up everything used.
If you put some time in, I think you can find a mesh head kit for close to the price of a new rubber pad kit.
The hard pads are not good for the wrists either.