I think your GLI would look more unified and more "upmarket", though you already have less of the black plastic to start with.
As for the price, it will really depend on what shop and where you are. It took me the past two months to find a shop that would do it, I finally chose one that does custom work on Lambos and Ferraris. The lowers were about $1000 (votex kit was $2500 painted and installed) the shark fin was about $300. There was a cheaper shop, but they wouldn't guarantee the work. I got a lifetime warrany with my paintwork.