That's a delicate question. My initial reaction is that I should probably have it capped lower, actually. My main failure mode with support zero is that I just forget about it. Derailing is almost never a conscious decision of weighing pro-and-con and deciding to pay, and so it tends to just feel punitive.
Now, I know that @dreev is going "well make it expensive enough and you won't forget about it!". I forgot about it at $270. And I can still remember pretty vividly how horrible that felt. So there's something wrong with this goal, but I don't know what. And it is really valuable for keeping things from starving in support.