Your employer group health insurance coverage, negotiated between your employer and Allstate, should be very different than what you find online open to the general public. Talk to your HR people. Ask for plan documents outlining your benefits, copays, deductibles, max out-of-pocket, network of doctors and hospitals, etc.
It would be very unusual for an employer to offer supplemental health coverage only. This assumes you have primary coverage elsewhere. Not usual business procedure, as yet.
If you learn your employer is only offering supplemental coverage, then, of course, you'll need to find primary coverage somewhere. In 2014, you can buy Obamacare through the exchanges. Estimated cost calculator, here:
Subsidy Calculator | The Henry J. Kaiser Family Foundation