gpoole there are a range of open source testing tools which have a zero cost of purchase. These can be found in various locations, with reviews at Danny Faughts opentestware reviews site. Many can be found to be down loaded on sourceforge.
Which tool is appropriate will depend on your goals for the tool and what type of tool you are after: Automation at the GUI layer, sub GUI testing tools, Performance testing tools, test planning, test/ defect management, test design, test data tools and so on.
A bit more context and the goals would help us to help you.
Also the five hundred dollar limit (US?) is this per tool or for all tooling? Is it also a hard limit or is there some flex in the upper range?
Wow, you're everywhere. Well, I am very new to testing (automated or not) but from your list, I am looking at Automation at the GUI layer, sub GUI testing tools, and test/ defect management tools. The budget is per tool.