As unpleasant as caffeine withdrawal can be, it might be worth going through to lower your tolerance and cut the cost of your habit. I would recommend you then use it moderately to avoid these financial issues, although the fact that they've gotten to be a serious issue in the first place makes me wonder how much of an option that is.
Oral caffeine use is rarely fatal, because long before they consume a lethal dose people get so sick--with blurred vision, confusion, tachycardia, headaches, severe nausea, and tremors--that they think they're about to die, promptly suffer a large panic attack, and call 911. A truly dangerous overdose could include seizures, hallucinations, and/or rhamdomyolysis in addition to the previous symptoms.
Caffeine powder is easier to overdo, but if measured out properly it can certainly be used safely. For this reason, it would be advisable to determine exactly how much caffeine you consume on a typical day and measure it accordingly. Cardiac arrest can occur at extremely high doses, but you're unlikely to ever consume that amount if you approach with it with any measure of caution. The previous statement goes out the window if you have a preexisting heart condition, of course.
Thanks; but what does happen if I accidentally take 1000 mg for instance? Do I just drop dead of a heart attack? Sounds like it might actually be a useful state to be in to get work done n stuff.
For someone with a low tolerance, it would probably be extremely unpleasant. However, energy drinks tend to have around 160 mg per can, so you might not feel quite as bad as I would. A heart attack is highly unlikely unless you already have other risk factors.
On the other hand, very high levels of caffeine can sometimes cause euphoria on par with other stimulants, if Erowid reports are to be believed. You're more likely to suffer the issues I mentioned above, though. And I doubt doing that regularly would be good for your heart. Or stomach. Or sleep.