I’ve made my own in the past. Mostly because I tried some pre-mixed stuff which cost about a tenner for 100ml and was mostly perfumes and base oil rather than essential oils — i.e. a ripoff.
Startup costs for going the DIY approach are reasonably high, largely because you need to buy the aforementioned essential oils, which can get expensive depending on what you want.
However, once you’ve got a set of oils you like, it’s cheap. Base oils vary in price a bit but will be ~£2-£3 for 100ml, less if you buy in bulk.
There are some considerations to be aware of when selecting essential oils since some may have negative impacts if used in too high a concentration on your skin. There are plenty of resources about this sort of stuff online though, so just read around.