Coil life depends on a lot of factors, including type of juice used (often, sweet or dark juices gunk coils, as does NET juices, high VG content juices and etc.) Airflow can play a role, and the higher the wattage used, often, the lower the life of the coil. It also depends on how much you are vaping, not number of days that pass....
The only way I know of to save on coil costs is to consider building your own coils. You are fairly new to vaping and also, coilbuilding and using a Rebuildable Tank Atomizer takes time and preparation, but it is a savings in the long run. If you are interested, you could head over to those set of forums and check out some pinned threads to see if it's for you. Or, if you want to save money elsewhere, you could look at the DIY e-liquid forum as DIY does save money after startup costs.
Some coils seem to last longer than others, but I don't vape sub0hm so I'm not much use to you there.
Good luck,
Anna