So, as one who is fairly inexperienced with bike tweaking, I'm wondering what I would need to do to convert to trekking bars?

I currently have an older Novara Randonee with drops and old STI shifters. As I understand it, these would need to go, right? Would I likely need a new stem as well? I'd really like to do this myself, but if it's over my head I guess I can just have the LBS do it. How much do you think I'd be looking at, here?

(It wouldn't be the end of the world if the STI's had to go, either. They're older, suffering some problems, and I've been really close to pulling the trigger on a cheap IGH anyway; I'm just not sure if I'll have the moolah to swap all of that at once)