SMS on the CRM is about 0.06p PER segment, so please try to keep your texts to a minimum so you don't get charged an excessive amount.
Type your message into: https://twiliodeved.github.io/message-segment-calculator
Check how many segments you've used:
Segments x 1 SMS = Total of 1 SMS (0.12)
Total of 1 SMS x How many contacts you want to send to = Total cost of your SMS campaign.