it all depends on what you need. Some software would need 30 licenses, some needs one license, some has "check out" licenses so if there will never be all 30 using it, you can buy less, like 20. Every software company will have different prices/plans/etc.
The server specs depend too. Does the software do lots of calculations or 3d stuff that will require lots of ram/processors? Will they be storing data on the server? If there will be data on it, do you want it to have an internal RAID, a RAID attached to it, or just an external or offsite place to copy it to? Rack mountable or desktop form?
Then there's lots of other stuff you can get. Most OEMs have things like Dell's iDrake which is REALLY handy for offsites. You can remote into the iDrake and watch it reboot, get into the BIOS, etc even if the OS won't boot or whatever. Kinda cool but more $.
So it all depends on what you really need brah.