I paid about $550 in parts for my retrofit. This included projectors, ballasts, bulbs, bezels, and misc. hardware used to do the project.
When people ask how much I'd charge, I'd say $600, including your lights. Most people think that's crazy, but when you think of my overhead for buying parts, I'm only charging around $50-$100 for labor.
Now, if you told me you wanted S2000 projectors or something, the price would go up, since they cost a lot more. Example: there are a pair of S2000 projectors on eBay right now going for $378. That's just projectors. Factor in another $80 for bulbs, and almost $300 for new ballasts (this is all "new" stuff) then approx. $50 for hardware, and you're looking at a tad over $800, and your headlights.
Obviously, things can be had cheaper if you shop around. I got bulbs for $60 off of eBay, and 2 new ballasts for $220 off of eBay, but one ballast ended up not working, so I got a half refund and was forced to pay $165 for a new one.
Why am I still rambling? Well, I'm trying to give you an idea of what things cost. The price for retrofitting would cost even more if, for example, you wanted to keep your headlights. That would leave me out a set, and I'd have to buy some new ones. That'd cost you at least $550 more. It sucks because our headlights are so hard to come by and therefore so expensive.
I'm thinking of selling my current retrofit after I tweak and perfect it a bit. If they come up for sale, I'll post a thread in the FS section. Sorry so long, just trying to shoot some numbers w/ ya.