I keep running out of RAM!

How do you know you're "running out"? If you're looking at inactive memory space in Activity Monitor, keep in mind that allocation is essentially the same as free. If an app needs more ram than can be allocated out of free area, it will use ram from the inactive space.

Also, look at page-outs. If that is low or zero, you really aren't running low of RAM. It's mainly when there is no available RAM from either free or inactive and the system needs to swap pages out to mass storage that will cause a noticeable slowdown.

This has a brief description on how to interpret what's seen in Activity Monitor: http://support.apple.com/kb/HT1342

 

Why do you think you need to use the purge command? There is nothing wrong, in itself, with having lots of inactive RAM.
You may have a problem if that Inactive RAM is not being released to Active RAM when needed, and if you are swapping out.

Activity Monitor in Mavericks does not give details about Inactive RAM usage, so it does fix the problem of worrying about it.

 

What program or programs are running at the time?

Post a screenshot of Activity Monitor, with "All Processes" showing in the list.