Which power supply should i use?

These are the official recommended power requirements for your GPU:

500 Watt or greater power supply with two 75W 6-pin PCI Express® power connectors recommended (600 Watt and four 6-pin connectors for ATI CrossFireX™ technology in dual mode)

This applies to the whole system not just your GPU.

The Corsair 650TX is a great PSU but doesn't have the four PCI-E connectors required for Crossfire on your graphics card. However the 650HX does have four connectors and is a modular PSU which will help keep your case clean and free from unused cables.

http://www.newegg.com/Product/Product.aspx?Item=N82E16817139012

+1 what moody89 said.

The Corsair TX650 is an older model. The HX650 is a newer model that has the required number of PCI-e power connections for the ATI Radeon HD5850 video card.

trying to stay below $70 for a new psu though...
should i just use the antec with a converter then and wait until i decide to crossfire and look for one?

meh, how about this one then?
Corsair TX750W, $80, has 4x 6-pins
i suppose ill just have to eat the extra $$$ then x_x

Thae TX750 is another excellent choice.

That too will be more than enough for your needs. I guess you'll have to spend the money at some point either way!