The only ways in which you can send SMS is if you have WiFi and it's sent through third-party applications and not phone applications, such as having credit on Skype and sending text messages through Skype using the credits. The other way is having a SIM card inserted into your phone and it's setup properly with enough credit in it or package that allows you to send text messages. In conclusion, you cannot send text messages without "money", without having WiFi or SIM Card. Hope my answer helped.
If you have a Google Voice account, then you can send texts to other numbers while on WiFi, and you'll receive texts, too. However, you have to have this already set up because you need a phone number to activate the account. Skype is always a solution as mentioned by Kyler. Then you can try apps like WhatsApp, Facebook Messenger, and even Viber. You'll be sending IMs rather than texts, so other users will have to have an account for a given service.