What is the cost of creating an EOS alias account name? And where can one create one? What prevents people from squating names?
There isn't a concept of "alias account names" in EOSIO--account names are unique identifiers, and they all cost the same and have the same functionalities.
Accounts cost network resources to store the necessary identifying data and metadata, so there is a RAM cost associated with creating a new account, making squatting names a costly process. Thus, each account must be created by a parent account that pays for the necessary resources.
The official documentation has an article on creating accounts on a testnet. Example command from the docs:
$ cleos create account eosio bob YOUR_PUBLIC_KEY