The most important aspect of using a monitor for photo editing is accuracy. Which means that no matter what you buy, if you want to know its a good reference point, you'll have to calibrate it. And you'll also need a monitor which provides consistency when you view it off angle, otherwise that calibration means nothing.
Set aside some of your budget for a calibration kit, such as this one
When calibrated and viewed in the best light (no direct light on the screen, ideally controlled colour temperature and brightness in the room), you'll be able to get an accurate idea about black and white points, as well as colour.
However, if you use a monitor such as your existing Samsung, the moment you move your head, the colours and brightness shifts. That is because it is has a TN panel, and like all TN panels it has narrow viewing angles. Stand up and everything will look brighter (in extreme cases, bright whites turn to mid grey), lower your seat and blacks will turn to mid grey. And move left or right and the colours shift. So it doesn't matter how much you calibrate a display like that, you'll never know if what you're seeing from whatever angle you're at is correct. While there are good and bad TN displays, even the very best fall a long way short of the accuracy photo editing demands.
Buying a monitor using display technology such as IPS is a good way of almost completely eliminating this effect. Backlight technology isn't too important, although many white LED backlights can have a cold blue tint, and not much in the way of red or green gamut. RGB LED backlights are very expensive but can give a very wide gamut, so old fashioned and much cheaper CCFL backlights might be your best bet, if you can find any around. Laptop displays tend to be worse off-angle than desktop displays due to the backlight diffuser concentrating the light straight on to improve battery life, while desktop displays tend to use a more powerful light and spread it wider.
Budget lines of IPS monitors tend to be the Dell Ultrasharp range, HP make some too, and various cheap brands which use the rejected IPS panels from the big manufacturers, such as Hazro. At the price point you're looking at, wide gamut isn't really an option.
TFT central is a great review site. http://www.tftcentral.co.uk/
Something like this 27" IPS screen from Dell
just about scrapes into your price range even when you add the cost of calibration kit. But there do seem to be bad user reviews about backlight bleed.
Your best bet is to read the reviews on TFT central and other sites to work out what compromise you personally want to reach on size/quality/price.