I certainly enjoyed using the Powerbow (Gray Nicolls) last season, SH, meaty, good at dishing out some big blows.
However, I've used it a couple of times this season at it doesn't seem to be middling as well, I think might have to oil this bat a little more regularly than your normal bat.
But when I used it last year, seemed to have a large middle and felt good. I would also recommend Woodworms if you consider anything else although I hear they might have gone out of business a couple of years ago?
I would check for weight as well, I haven't really been doing much exercise over the last few months and the bat feels a lot heavier than it did last year!
I personally buy GM, I bought the new Flare 808 a few weeks back and it's an absolute beauty.
If you want Gray-Nicolls though, I had a net literally a few days ago with my friend's Oblivion and it is a wonderful bat. Got quite a low middle, so if you play on bouncy wickets frequently, probably not for you - but it is fantastic! (Also SLIGHTLY over your budget with this website, but hunt about a bit and it's around £200!)