The I-134 is a contract between the sponsor and the US government stating that the sponsor will be responsible for the visitor/beneficiary while the person is in the US. Make sure that the sponsored person has sufficient financial support for the time period of their stay. I.e. basic amenities to support their living and welfare in US. This includes: food, boarding, clothing, & health care.
For possible healthcare expenses arrising out of illness or accidents, it is a good idea to get a good visitors' medical insurance.
You can find more information in the following link: US Visa Sponsors Liabilities: Whether the Sponsor is Liable for Visitor’s Unpaid Bills?
Insurance rates are regulated by law. You can't find the same insurance plan for a lower price anywhere else