i will warn you about water issues/peeling clear coat issues on aftermarket impala headlights. spyderauto is a reputable brand with great customer service that i personally used and had great results. several other guys could vouch for them as well. the cheaper lights i tried just didn't hold up well or fogged badly.
pick your light you want then search for the part numbers on ebay or amazon. they are pricey but you get what you pay for. installation of the halo's is actually pretty straight forward and easy. i even used spade terminals on my connectors to make the headlights pretty easy to pull after installation. just shrink wrap the connections to keep water out.