http://www.amazon.co.uk/Yamaha-F310-Acoustic-Guitar-Starter/dp/B000I1V5KA
The Yamaha F310 is the best, cheap acoustic I've ever played. It's got a sound that can match much more expensive acoustics. I'm not sure if they do a left handed version, but I wouldn't be suprised if they did.
Most acoustic guitars that sound really good cost a lot of money. Cheaper acoustics use laminated wood, which doesn't sound as good, or mature with age like a solid top guitar.
Here's some information about the difference.
http://www.sheehans.com/acoustic-guitars/help/#solid
I'd be amazed if you can find anything better than the Yamaha F310 for anywhere near the same value.
It all depends on what type of music you want to play on it mostly, which will define which type of guitar you need to go for.