There's a lot of good information about both xenon and HID lights by Daniel Stern Lighting.com.
Basically Xenon bulbs will fit in the stock housing like a stock bulb, HIDs (depending on which one you get) will require some modification. Some kits are cheaper than others, but note that HID lights should not be put into stock reflector housings.
There are a few newer stock replacement bulbs that are designed for motorcycles and work very well in the Ninja 250 and don't cost much.
I have the Phillips MotoVision Motorcycle Bulb
H7 bulbs. Its an excellent stock replacement. Quite a few members on other forums use them. They also have great reviews in the motorcycle community. They may also be cheaper than the ones you are considering.
The light beam is white, goes out further and is about 40% brighter than stock. There is a very slight orange glow in the reflector, but you have to be on the right angle to see. It also shows on the ground at the trailing edge of the light beam closer to the bike.
Here is what the Phillips Motovision looks like on high beam during the day shining into a camera lens.
You may be able to find other inexpensive H7 headlight bulbs that are brighter compared to stock but maybe more expensive or lower quality.
Philips is known for making very good lighting products. Some others are listed below.
PHILIPS MotoVision Light Bulb ( attached pic is bulbs installed on my bike)
PHILIPS Xtreme Power H7
Philips Blue Vision
Bikemaster Vision X H7 Bulb
GE Nighthawk H7-55NH/BP
Sylvania SilverStar Headlight Bulb