It depends on the max and RMS wattage of the subs. For example, if they are 2 500watt max subs, the RMS might be 200 on em. You could run a 2 channel 600 watt amp (300x2 peak) or a 800 watt amp (400x2 peak).
Use the best wiring you can, and get a head unit with the features and look you want. If you just need a bit of bass, you may want to use just 1 sub. Brand of sub may matter at a serious or competition level, but if you just want some bass, it really doesnt matter, but try not to go with a generic from a small company. Kicker Solobarics (the square subs) are nice.
Dont be cheap when it comes to buying your speakers, and make sure you get at least 1 pair of tweeters.
Almost everything is cheapest on eBay, but you might want to order your wiring from Crutchfield and get one of their installation diagrams for your specific car, it comes in handy.