You can spend as little or as much as you want, from an old beat-up Graphic with the original lens/shutter for maybe $100 total,
to a large kit with numerous lenses, each of which costs thousands of dollars.

I would strongly recommend you start with an inexpensive used camera and a decent lens with a modern shutter (this is important).

The 'normal' lens for 4x5 (equivalent to a 50mm on a 35mm camera) would be 135mm to 150mm.
The most common aperture for LF lenses is f/5.6, but some wide-angles are larger, and some long FLs are smaller.

Read the introductory pages at LFPF (http://www.largeformatphotography.info/) for a good over-view of the topic.

- Leigh