What kind of PSU could I get away with?

I was wondering what was the minimum wattage I could go with for this build. Could you tell me how much more power I would need if I added another 4850 in the future as well?
CPU: e8400 @ 3.6
RAM: 4 gb (2x2) Corsair 1066 RAM
Mobo: Gigabyte GA-EP45-UD3P
HDD: WD 7200 RPM 32 mb cache
GPU: ATI 4850
Case: Raidmax Aztec
Please, if you can, tell me how much power I'll need for both one 4850 and 2 4850's. Links to suggested PSU's would be appreciated as well. (I'm only doing this to see if I can save a bit of cash until I can buy a better PSU, so suggestions should be kept as low as possible in that area ) Thanks a ton, this really helps me out!

From HD4850 manufacturer

"Minimum System Requirements

* PCI Express® based PC is required with one X16 lane graphics slot available on the motherboard
* 450 Watt or greater power supply with 75 Watt 6-pin PCI Express® power connector recommended (550 Watt and two 6-pin connectors for ATI CrossFireX™ technology in dual mode)
* Certified power supplies are recommended. Refer to manufacturer website for a list of Certified products
* 1GB of system memory
* Installation software requires CD-ROM drive
* DVD playback requires DVD drive
* Blu-ray™ / HD DVD playback requires Blu-ray / HD DVD drive
* For a complete ATI CrossFireX™ system, a second ATI Radeon™ HD 4850 graphics card, an ATI CrossFireX Ready motherboard and one ATI CrossFireX Bridge Interconnect cable per board (included) are required."

http://www.newegg.com/Product/Prod [...] 6817341010