I suppose in a perfect world with unlimited funds, we would all practice with $1 per round carry ammo. However, I don't live in a perfect world and I darn sure don't have unlimited funds. If you don't reload, all you can do is find some reasonably priced practice ammo that comes close to the bullet weight, velocity, and recoil of your carry ammo. At reasonable distances, let's say under 25 yards, you should have a close point of impact to your carry load.
Many of the American ammo companies sell a fmj practice load that closely matches their carry ammo (Speer Lawman and Gold Dot is one example). My opinion is that these practice ammo lines would be the closest thing to the self-defense ammo you could get without paying for the real deal.
In the end, I would much rather shoot a few thousand rounds per year with practice ammo than limit myself to shooting a few hundred rounds of carry ammo because that's all I felt comfortable using to practice.