Almost all store bought air fresheners are synthetic scents these days. Not only is it pricey to have to keep buying these, but these synthetic fragrances are not good for you. They often either coat the interior of your nose with an oil film or use a nerve deadening agent to mask odors. They are starting to be linked to potential lung damage and asthma and are especially bad for children.
One alternative is using essential oils. I often do this for our home. You can simply take an essential oil of choice and place one drop of it on your bathmat (be sure to do a color fast test on the underside of the rug first - though, I have never had an issue with staining). Be sure to keep the bathroom door shut as this will keep the scent confined to the bathroom. For those with children, use a kid friendly oil such as lavender, lemon, grapefruit, or mandarin, and these are inexpensive oils.
It is important that you buy organic oils from a reputable seller, especially when you have children, as adulterated and non-organic oils often contain toxins that can be harmful. (Organic is very important when it comes to essential oils because they are so concentrated that if they are not organic, the pesticide concentration will be very high in the oil.)
Be sure to rotate your oils, as it is never good to use one oil over a long period of time.