Carl Dun :
I live in the Philippines and it costs PHP 6,200 (around $138) and the two nearest to its price range are:
1. ASUS GEFORCE GTX 750 1gb (PHP 6,000, around $134)
2. MSI GEFORCE GTX750 (PHP 6,650, around $148 )
Those two video cards above have 1gb ddr5 128bit specs as opposed to the 6790 video card that has 256bit. Although I'm not sure what else does these other two might have that makes them cost more or its just that the 6790 is just cheaper.
Architecture, software compatibility (ex: DirectX 11.2 vs DirectX 10), GPU cooler, design, quality of the company, overall looks...
Also, not all video cards are meant for gaming; that being said, some cost way more than others, but would prove useless in gaming than others...
For example, take a GTX 750Ti ftw Edition that cost around 150 US currency.
And then take this VisionTek video card that cost 239 US currency.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814129274&cm_re=video_card-_-14-129-274-_-Product
The difference is that some video cards are meant for a complete different lifestyle than others.. Where the Visiontek is meant for low profile workload that could easily handle up to 6 4k monitors (YES SIX 4K MONITORS!!!!), and the GTX 750 is meant to handle gaming at moderate resolution (moderate compared to 4k of course)