The cost of glow plugs? Cummins don’t even have them.
Most additives don’t hold up under scientific scrutiny.
The only real-world extra cost of having a diesel is the buy-in.
And it’s a lot. It mostly depends whether all the extra torque is worth it to you.
Depending where you live, you can delete all the emissions junk and DEF tank and all of a sudden you have a truck that runs great, gets good mileage and doesn’t suffer most of the problems the new ones generally have. Save all that junk in the garage and put it back when you sell it, IF the next owner even wants it.