Official training is available but attendance of a course is not mandatory in order to obtain a PSM certification. The assessment itself costs $150 to take separately (the fee is typically included in the cost of any training courses).
You can download the official Scrum Guide for free from the Scrum.org website and they also provide a free Open Assessment to evaluate your readiness for taking the real test. The Open Assessment is the exact same format as the real assessment and is taken from the same pool of questions so it's definitely worth spending an hour or two on to become comfortable with the format.
The PSM assessment:
- Must be taken with 14 days of purchasing a password
- Requires correctly answering 68 out of 80 question to pass (85%)
- Has a 60 minute time limit and cannot be paused
- Consists of multiple choice and multi-select questions / answers
- Failure requires purchase of an additional attempt