I found a place online to buy prescription rayban aviators. They worked out cheaper than buying a set of normal raybans. Unfortunately i cant remember the name of the site but im sure Mr Google could assist should you check with him.
I wear my sunglasses regular as it does get pretty bright in the cockpit. The ones i have are made with really skinny arms which are perfect for peripheral vision and also still allow your headset to seal perfectly round your ears.