Generally speaking, a 2007 Honda Civic SI turbo kit is going to cost anywhere from $1,200 to $4,000, depending on the seller and the quality of the turbo kit itself—and the highest quality kits can actually range closer to $5,000 - $6,000.
eBay and sites like it are going to be where you’ll find the cheapest 2007 Honda Civic SI turbo kits, ranging between $1,000 and $2,000.
If you have a little more money to spend, however, you might try sellers like Affordable Turbo Kits or Vivid Racing, as their turbo kits usually sell for between $2,000 and $3,800 and are of a higher quality.