What is the price point cut-off for the customer?
At what point can the customer no longer afford to install or maintain the authentication solution you're suggesting? There's a limit, but you need to understand where that limit is so you can price your solution within those boundaries. Bear in mind that the costs of a solution aren't just limited to the initial installation and configuration. There are often years of behind-the-scenes costs related to patching, maintenance, upgrades and experienced human resources for administration. Try to choose solutions that offer as little change to the customer's current IT operations as possible in order to limit the learning curve. Look for solutions that will fit well with the existing skill sets, so the customer doesn't have to hire new employees. Consider offering on-site training for the solution to the customer as well, to limit training costs on the new solution.