if it's bone stock it must be the 1.6L engine. I would not recommend that your friends buys a CAI cause it'll be worth 600$ or more. Build a custom one yourself, it'll come way cheaper.
depends for what car. On a honda civic, you'll get them for around 230$ because they sell a lot of those. But they don't sell a lot for protege's, so that's why they're more expensive.