Modernizing Old Bianchi
 

So I bought an old Bianchi Tangent a few years ago and I am now becoming more of a biker. This bike is a hybrid and I use it mostly for road biking. I was wondering if it would be better for me to modernize this bike with new handlebars, new gears, and everything new required to add those parts or to just buy a new road bike? The guy at the bike shop said that it would cost about $500 to get all of these changes done.

If you could take a picture of the bike and post it, that would be helpful. It's hard to say whether you received good or bad advice at the bike shop. First they base their fees on all new equipment. Second, some of them don't like to work on older bikes so they jack up the repair bill then hit you with, "You'd be better off with a new bike". Which they would be happy to sell you. And some like to repair old bikes and give honest repair/replacement prices and sometimes use older/used parts to lower the costs.
It's hard for us to evaluate based on the limited information you provided and no pic.