[feature] added "getPurchasedServerCost" NS function

doc/source/netscriptfunctions.rst

@@ -670,6 +670,21 @@ purchaseHacknetNode
     end of the Hacknet Node's name (e.g The Hacknet Node named 'hacknet-node-4' will have an index of 4). If the player cannot afford
     to purchase a new Hacknet Node then the function will return false.
 
+getPurchasedServerCost
+^^^^^^^^^^^^^^^^^^^^^^
+
+.. js:function:: getPurchasedServerCost(ram)
+
+    :param number ram: Amount of RAM of a potential purchased server. Must be a power of 2 (2, 4, 8, 16, etc.). Maximum value of 1048576 (2^20)
+
+    Returns the cost to purchase a server with the specified amount of *ram*.
+
+    Examples::
+
+        for (i = 1; i <= 20; i++) {
+            tprint(i + " -- " + getPurchasedServerCost(Math.pow(2, i)));
+        }
+
 purchaseServer
 ^^^^^^^^^^^^^^