http://shop3.outpost.com/product/4470306?site=sa:Homepage:Spot1 and will my Antec EarthWatts 500W Power Supply be enough for it
Yes, but I would recommend changing power supplies, EarthWatts is not a brand I recognize.
Also, great choice on the P180, awesome case.
then which power supply under a 100 is good?
Antec NeoHE or TruePower (if you want to save and don't need modular cabling) 500W will do the trick.
Edit: Just saw that EarthWatts is not a brand and in fact a subdivision of Antec. If you want to be eco-friendly, go for it, otherwise I still feel the two aformentioned PSUs are superior.