*NOTE* UV LIGHT CAN BE DANGEROUS TO YOUR EYES!!!!!!!!!
That being said:

I've ordered UV LEDs off of ebay from Hong Kong usually you have to buy a fairly quantity like 50 or 100. Mine came out to about $0.30 a piece. These UV LEDs require 3.4-3.6 volts and use need to have the current limited somewhere in the range of 30-50ma (30 - 50 milli-amps). I have read somewhere else on Instructables that you could get them out of a device used for brightening teeth.

To drop the 5V USB power subtract 3.6V from 5V = 1.4V this voltage needs to be 'dropped' down using a resistor. Which also limits the amount of current flowing through the LED. Dividing 5V by .05 Amps (Ohms Law) gives you a value of 28 ohms for the amount of resistance.

I believe USB power supply is current limited meaning that it is a "stiff" current source so you might be able to use a lower resistance like a 10 ohm resistor. I'm not a 100% on that so don't quote me.

As for connecting it the link in a previous post gave a nice tutorial on how to build this type of device.

Be sure to observe polarity, connect the cathode side of the LED to the negative wire. If you don't know what this means read up on it.

Any further news on this project?

Start here:
http://www.instructables.com/id/E1OSW5LM9YET9K4IMM/.

You'll need to make sure the values are consistent with UV leds as well. You'll probably want to use a cheap usb cable for the connector and to place the leds. Not sure what you meant by using a cheap cable extender - did you mean you wanted to plug this in, and still be able to use the usb port? You might be able to get away with it, but only if the devices don't draw much current.

Good luck!

what you could do is velcro a match box containing the uv led to the top of the screen and wire it to the usb by destroying an existing cable. you only need the red & black cables. usb is 5 volts, you can work out what resistor you need when you get thee led. its not the most pretty solution, but its all i can think of

if you get a usb extension cable and cut the female and off, you will have a green a red a black and a white wire. you only need the red and black, this is your power source. you can use this http://www.instructables.com/id/E9NFEFO2ZGEV2Z9QKZ/ too wire up the leds because i dont know what to do with the leds, so im gonna have to read that aswell