It's not so much the particular dollar amount, but that it sounds like your process for evaluating whether a tool is "essential" is basically "whatever the boss feels like in any given moment" instead of having a transparent evaluation process that weighs, say, $10/yr/employee vs the potential for risk for malware/ransomware or even simply lost productivity from intrusive ads. Is there ANYTHING an employee should be able to spend money on without your direct approval? Is there a process for evaluating what is an essential business expense, per position? How small a business is yours?

It's the lack of agency and trust in your people, rather than the specific dollar amount, that bothers me. If it was a $10,000 or even $1,000 purchase (such as buying that ad blocker for the whole company), yes, of course it should merit more evaluation, but is there really a need to micromanage every single transaction instead of having an expense account of some sort and a procedure for small purchases and reimbursements?

Not arguing that all your employees should be able to arbitrarily spend company funds willy nilly, just that they deserve some say in how they do their jobs, and the tools they need for it, instead of being simply being told "no, because if we scaled that $10 up to all the X employees it would be too expensive..." Did all the X employees even ask for that..?