We can't do everything for you, you have to do alot of searching for yourself
what we can help you with is this:
1. to find the prices, if you're american: go to newegg.com
2. use google
for the typical ones: HD 5830: 175 Watt
(the ones you want for mining) HD 5850: 170 Watt
HD 5870: 188 Watt
(note that when overclocking, they'll need more energy)
http://www.pcgameshardware.com/aid,705500/Ati-Radeon-HD-5830-reviewed-New-price-performance-king/Reviews/for others, just type in the name of the card/processor/motherboard/etc in combination with energy consumption or watt you'll find it
3. very.
If you've already red the articles, you'll know that you don't want Nvidia, you want ATI.
the card you want is dependent on the price you can get it. the best choise in my opinion is the 58-- series, because they are usually the most for your money
if you want to mnow more, just ask