I make my own using a combination of citronella, eucalyptus, peppermint, and a few others. At first it costs more when you buy these essential oils. But you don't need very much and I'm on my 3rd year of them...so now it's cheaper.
I use a carrier oil of grapeseed oil - but you should also use a alcohol - like vodka - or something called polysorbate (aka Tween 20). I'm not able to find that around here, but it can be purchased on-line. so I've just used the good ol' fashioned alcohol.
There are lots of recipes on-line - and mine is my own concauction now - a dab of this and a drop of that.