Same gpu diff price

AMD makes the card, but other companies such as Sapphire, Gigabyte, MSI use the chipset and make the card. Differences are overclocking capability, some will overclock better than others, temperatures, and noise.

Try googling, reference and non-reference video card. From there you would be enlightened. Summary would be like,
Reference video cards, would be cards made by amd, then companies would just like put a sticker or something on it and would sell them, and what would matter would be warranties and the likes.
Non-reference video cards, usually these are those that you would see with dual fan or more. The companies would use the same gpu and sometimes change the board and stuffs to improve performance and would also put their own fan/cooling solution on it to improve cooling.

AMD does not make the card. They make the GPUs and design the card but manufacturers like MSI, Sapphire, ASUS and the rest can redesign them and they are the one who actually manufacture the card.

@Tylerlu97

The price differs because they use different components around the card and have different designs and sometimes they come factory overclocked as well. Cards that have coolers like MSI's Twin Frozr or Sapphire's Vapox-X are bound to have higher price (sometimes it's the same or lower as well) but they cool better than reference design card that uses the single blower fan cooler.

how will i know which gpu will b the best if they are the same but made by diff manufacturers?

That's why there are reviews and benchmarks and such. The GPU (ie. the HD7850) will all perform quite similar. It's just that the different cards and coolers affect the overall temperatures, noise and overclocks. It all depends on how well the cards perform (in terms of noise, temps) and how much do you trust the manufacturer (support, warranty). Anyway, here are some charts and roundup to help you compare.

- http://www.tomshardware.com/charts/2012-vga-gpgpu/21-Te...
- http://www.tomshardware.com/charts/2012-vga-gpgpu/25-No...
- http://uk.hardware.info/reviews/2853/13/amd-radeon-hd-7...