Help with stroller and pack n play buying

I'm trying to buy my baby sitter a stroller and a pack n play and I can't seem to find a cheap one in my town that matches the brand of her carseat so I was wounder if any stroller will let baby trend snap in or will I need to get some straps to make sure the car seat won't move or fall off the stroller.....and is their a site I can buy them used and get shipped to my house?