Most 2013 Civic SI turbo kits cost somewhere between $2,100 and $4,250, but the most expensive kits can range closer to $6000—and as you can probably guess, the higher the price, the higher the quality.
That being said, it may be possible to find cheaper options (think $1,000 to $2,000) if you decide to buy a turbo kit off of second-hand seller sites like eBay—if you do decide to go this route, be sure to exercise caution and make sure the seller is legit.