I'm pretty new and don't have the terminology down yet, but I use an ego with a Pyrex Aro tank. As I understand it, the bottom part of the tank contains the atomizer and a coil. They told me at the vape shop that I would need to replace the coil every so often, so I got a pack of 5, but they cost $2 each, so $10. That seems pricey to me. I don't know how often I will need to replace the coils.
When you say "cartos", would that work with my set up and be cheaper to replace?
The Aro looks very similar to the EVODs and such, which I have, and seem to last pretty long with a little care. It all depends on the type of juice you're using, how "clean" it is. There are some out there, like tobaccos, that might have some particulates in it that will kill the coil. Also, there are some sweeter juices that do the same. Personally, I've never had any problems, but my experience is rather limited.
What do I do to make my heads last longer? When I change flavors, I pull the old head out, rinse it with hot water, then sit it in a shot glass full of water to soak overnight. Some use everclear, vodka, etc, so what you use is really up to you. I find water works the best for me though.... Right now I've got about 8 heads, all of them are used. 2 are in current setups, 2 need to be soaked but I'm lazy, and 4 have been cleaned. The last time I've bought heads was probably 6+ weeks ago, the oldest ones are probably 3+ months old. When they get a funky monkey .... taste, they get tossed.
As far as cartos and carto tanks, I've just started down that road, and they're awesome. I can chainvape without any dry hits. Cartos can be cheaper in the long-run if you buy in bulk, I think I've seen them for less than a dollar per carto, but you're buying 50 at a time. But doing that, you're set for quite a while!!