Think if you as a Project Manager really need to buy a project management tool. I do not mean to say that a tool is not important to manage projects. It is. A good tool is always helpful in optimizing your efficiency, productivity and accuracy. Tools with higher level of automation produce higher results. Now before you start exploring a new tool in the market after you have identified the need of it, it is better to look around and get a stock of situation with existing applications/ tools existing in your portfolio.
Have a complete inventory of all products that are deployed and running in the organization for years. What all legacy software and business applications are there in place need to be examined if there is similar kind of functionality/ tool existing that is required for monitoring and managing projects. ERP, for instance, might have that module, though not activated or configured so far, as there was no need of it; but which can be activated to draw out the desired benefits.