I've personally discussed this same power requirement with Steve Mantz of Zed Audio and for the $$$ I would buy the Zed Audio Minilith. It will do 600x1 @ 1 ohm. He quoted me $34 USD to ship to Alberta but just shoot him off an e-mail and he'll get back to you. If I remember correctly, the amp is only around 240 USD and they are strappable!!! You then have an option to go to 1200 w RMS for another $240 us. www.zedaudio.com

One major cautionary note!!! Before running an amp at what you THINK is 1 ohm, make sure that the subs are really dual 4 ohm and not actually 3.5 or something. This is how most of these amps get fried!!!

Either than or I would buy a used HCCA 225 or Soundstream Reference 500 ole school off ebay. Either one will (in my opinion only) beat the tar out of the new stuff and be cheaper doing it. 225's are going for around $150 US and refence 500's are in the 160 range right now I think.

The Zed, HCCA and Reference are all rated conservatively at 12 volts while I believe most of the new stuff is really @ 14.4 volts. To make a fair comparison, add around 20% to the 12 volt numbers as well.
Just my 2 cents.