Alright, just wanted to make sure you don't concentrate too much on performance when looking for an HDD. For your purpose, any HDD will be slow. Since you have no alternative; look at price and future upgrade plans.
If you need a 500GB system disk, SSDs are still very expensive yes. My own system disks are 8GB large thus a 40GB SSD would fit 5 workstations. In essence, i share my ssd across all workstations.
In your case you have a lot of games. A nice alternative would be to get a small 40GB Intel SSD for the system and use a big 1TB HDD for your games.