How to calculate the needed encryptions in salted passwords? Consider if a 16-bit salt is used, and it is uniformly applied over a very large password file (200,000 entries). An attacker wants to see if one particular password (say, "bubba") is used by any of the password entries. How many encryptions must be calculated, and how many comparisons must be made (of their generated-hash vs. stored hash values)?

Assume the attacker has the stored-hash-values, but he does not know which salt is used for any individual password hash. In other words, they can see /etc/passwd (so they know the 200,000 usernames), and have only gained access to the hash (but not the salt-portion) of what is stored in /etc/shadow.
In your case, you say the salt only has 16 bits of entropy, which is pretty weak.

To see whether 'one particular password' was used, the attacker would have to attempt 65,536 possible Salt combinations, for each 'particular password' that must be tested. The number of users does not  matter because we have now established a need to brute-force the (weak) salt, and only try a single particular password.

On the other hand, with a properly implemented modern Password Hash, where sufficiently strong (e.g. 72 bits of entropy) salt is used, if the attacker fails to acquire the salt, then there would be no practical way for him to brute-force the hash.