Cost depends on your location, LF cameras are much cheaper in the US compared to the rest of the world particularly Europe, Australia etc.
The best place to buy is probably here on APUG or the LFP Fourum Leigh's mentioned. However I'd recommend finding an LF user near you and looking at a few cameras first then decide and then sit patientlt for one to come up for sale. Better still place a wanted advert.
To give you an idea though I can & have put together LF outfits for less than £500 ($750) here in the UK, you'd possible do the same in the US for $500-$600. (Super Graphican 3 lenses but a lot of waiting buying at camera fairs - slight restoration).