You might be developing a new web application and you've got the suspicion that you might be having some sort of memory issue somewhere in it, as every now and then you're forced to restart the appserver in order to keep things going.
If you want to figure out what's wrong with it you might need a tool that repeatedly invokes it so that in the meantime you can monitor the JRE with something like JRockit's mission control.
If you need to quickly find a cheap solution to run lengthy loadtests while simulating a low number of virtual users, you should consider Proxy-Sniffer free edition and GCLoad's Amazon AMIs.
You can prepare your loadtest at no cost and even run some shorter tests (up to 10 minutes) by using the free version of Proxy Sniffer. If you then need to run a longer loadtest to further investigate your issue you could consider using the 5 VUs AMI (costs only 1$/hour) or if your development machine can handle the load the 100VUs AMI, which might allow you to quickly reproduce the issue.
The most important thing is that you can start using Proxy Sniffer without having to worry about raising purchase order or going through lengthy approval processes, assuming you'll be using it for a fairly short amount of time to start with...