When you say new you mean new to you and thus second hand. You'll only get BSO full sus for that money new.
I'd say what Wookie says is a good choice or anything from GT.
I concur with Mr Wookie too. I spotted 2 East Peaks that failed to raise £50 a piece earlier this year on eBay, both 100% complete and very underused judging by the pix. The frames are really light and strong, you might want to budget a bit for a fork upgrade and check the air shocks, I had one fail suddenly. If you buy just the frame, try to get the rear shock with it as it is a size that is becoming harder to find as a coil shock. Some of the air shocks cost your budget new.
Bit of patience should net you a decent quality bike for that budget, my favourite hunt would be Gumtree for a local pickup garage find that needs a little fettling.
I'd keep away from any GT XCR Idrive thing. They'll be within budget but are no fun at all. I got one in 1999 and it put me off bikes for 6 years!
I'd get the most modern bike you can as technology has moved on at pace. Don't know for sure but wouldn't be suprised to see a Boardman FS coming in around £300 second hand?
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