Do lots of people get sarcoma, or is it unusual?

Not too common. There are about 12,000 new cases of soft tissue sarcoma every year in the US - so yes it is not a common cancer.
Fairly uncommon. Sarcomas are cancers of connective tissue, like fat, muscle, ligaments, and bones. The more common type of cancers are carcinomas, which involve organs like the breast, colon, liver, prostate, lung, etc.