gistfile1.js

var data = {
        "product": [
            {"active": 1, "name": "MacBook Air", "price_us": 999},
            {"active": 0, "name": "Mac mini",    "price_us": 599},
            {"active": 1, "name": "MacBook Pro", "price_us": 1299}
        ]
    },
    SEK_USD = 6.57,
    res = JSON.search( data, '//product[active=1]' );

res.each(function(p) {
    p.price_se = Math.round( p.price_us * SEK_USD );
    console.log( p );
});
// { active=1, name="MacBook Air", price_us=999, price_se=6563 }
// { active=1, name="MacBook Pro", price_us=1299, price_se=8534 }