The cost of such insurance depends on your age but it's by far the cheapest form of insurance available. Normally it covers death and total permanent disability only. Some covers critical illness as well but you will need to confirm this with your agent. There are some policies that you can buy the critical illness as a rider of the term plan. Read more on critical illness.
If you wanted to be covered permanently but is currently can't afford to do so, try finding a term insurance with convertible option that allows you to convert it into permanent insurance without the need to prove that you are still healthy. As in as long as you gets insured and remains insured for the term insurance, you can convert it into a normal life insurance that has cash values built up on the dates available for conversion.
