Around how much should this nikon flash cost?

I'm fairly new to cameras but I plan to do A level photography next year and I'm getting the grip of it. My parents bought me a seconed hand camera for Christmas, a Nikon D70.It came with everything apart from a flash bulb.
All I need to know is a few things;
1, What is the termonolgy, do I just call it a screw on flash bulb?
2, What 'bulb' would fit onto my NikonD70?
3, How much should this cost?

Are you trying to say that the built in flash of your camera isn't working? If you're looking to replace the flash tube, you need to consult the service manual. Taking the flash unit apart requires skill and can be dangerous due to the high voltage around the flash tube (around 400V).

Or, you didn't realize that the D70 has a built in flash and you haven't looked in the manual to learn how to activate it? See page 94.
Manual can be downloaded at:
http://support.nikonusa.com/...a_id/13140

Or, you want to add an external flash to your camera?
In this case, you will want to look at the SB400, SB600, SB700, SB800, SB900 series of Nikon flashes. The SB400 is slightly better than the built in flash of the D70 and only allows the head to swivel in one axis. There are other manufacturers of flashes which will work with Nikon cameras, but you'll need to research those on your own.
SB400: about $120.

SB600: Discontinued recently, but you might find stock on this flash. About $225. Some dealers are charging premium price for this flash since it's discontinued. Don't pay more than $225 for a new SB600.

SB700: about $330. This flash is newly released and replaces the SB600.

SB800: discontinued, but you might find one second hand.

SB900: about $450. Top of Nikon's flash line.

If you want to learn about Nikon's flash system:
http://nikonclspracticalguide.blogspot.com/2008/01/nikon-flash-two-separate-metering.html
This is probably the only good information out there on how Nikon's flash system works. Nikon doesn't give this information.