You bring up one of the points I was hoping would be discussed:
If you do have a stockpile of ammo, and know how much ammo you have, you can regulate how much of it you use based on factual information.
You mention the cost of ammo in the past: this is another point I was hoping to make. When ammo is cheap, you pile it high and deep. Prices only continue to go up on everything. Don't be the guy that buys 50 rounds, goes out and shoots it, and returns home empty handed. I used to buy some ammo every payday. And just like a savings account, I tried to have surplus so I could build up a supply for leaner times. How much surplus you try to achieve was the question originally posted: if you actually managed to buy and save enough ammo to last for the rest of your life, then the current availability or price of ammo doesn't matter.
So how do you support your shooting habit: well, that isn't easy. But, part of the answer is that you do it just like you would build up a savings account or a retirement account. You add a little on a regular basis and eventually it adds up. Another thing for me is that I only have a couple hobbies: but, I am keenly interested in those couple hobbies. I don't have a Harley, I don't have a boat, I don't have an RV, I don't have ATVs, I don't go on expensive vacations..........my spare money goes into these couple hobbies. And, if you think about it, how much ammo could you stockpile away for the price of a Harley ? I am in no way knocking people that buy these things; that is what THEY are interested in and they are having fun. I am just pointing out that I am not into those things and thus have the money to spend on the things I am interested in (just like they did).