I've mentioned several tools that we use here, many of which cost money. We're very lucky here that we can have most of the tools that we want, I know it pains the check writers--"What? Another $300s per dev?!?!" but thankfully they understand that it helps us immensely. I can't help but notice that occasionally people will mention on their blogs that they really like a tool, but that their company won't buy it for them. I think that usually, that shows a bit of shortsightedness in their management.
Developers are expensive and impatient. Good developers are often even more expensive and even more impatient. Tools help developers write more code faster, better, and with less distraction. We'll use ReSharper as an example to try and calculate true cost of the tool.
Let's say a developer's salary is $60,000 per year, that's about $240/day, or $30/hr. Say you build 10 times in an hour, half those times, you accidently typo'd something so you have to rebuild. We'll say fixing/rebuilding costs you 2 minutes per hour. That's 16 minutes per day or $8/day, $40/week, or about $2000/year. All for losing 2 minutes per hour. It's worse than that too, because 2 minutes is a gross exaageration, and that 2 minutes is during a developer's most productive time... the time they actually spend producing.
Now what if, for $300 you could have something that would warn you of impending build errors, so that you could fix them before you actually built? What if it had keybindings (I use Ctrl+Shift+N and Ctrl+Shift+P) to skip to the next error so you can quickly correct it? What if it saved you not only those 2 minutes per hour, but also gave you several other nifty features that saved you time with navigating, formatting, and several other things. Would you spend $300 to save $2000 per year? I would hope the answer is yes. Many other tools share this same productivity boost to cost ratio.
Does this mean developers should have carte blanche for tools? I don't think so. There still needs to be some filter in place, some time for evaluation, and someone who is in tune with both a developer's need for a tool and the company's need not to spend money senselessly, but please, managers, seriously consider requests for tools.