That might be a bit low. At your lower end, a 300 mhash/s graphics card costs just under $150 let alone an entire rig.
butterfly labs 5gh/s for 274
But butterfly labs rigs are going to ship in a year at best, and it's a scam at worst. You can't compare butterfly labs pricing to anything else on the market because there's simply no comparison save for Avalon chips. But you sound like you want to buy a premade rig.