You ask a question that's on the minds of many people, as they arrange for help. Rates for in-home caregivers vary greatly, in part based on the services they provide.
Caregivers with nursing skills, for example, usually get paid more than personal attendants or companions. Caregivers who do heavy cleaning may earn more than caregivers who aren't expected to do much cleaning. Salaries also vary by location. To find the going rates in your parents' town, you'll need to do some sleuthing. But I'll provide some tips to help make this quick.
In general, caregivers earn at least minimum wage and often more -- sometimes much more. The Federal minimum wage is currently $5.85 an hour. States can have their own minimum wage requirement, so you'll need to check with the state where your parents live. Here's a list of state labor departments you can contact for this information. Minimum wage is usually the starting point; it goes up from there. To find the salary range of caregivers in your parents' area check the Eldercare Locator, an online tool (or phone service) that finds your parents' Local Area Agency on Aging. This government agency provides all kinds of local information on caring for seniors (real people via the phone), which should include caregiver salary range. You can also try calling local senior centers to ask for their input.
One more thing: If you hire from an agency versus on your own expect to pay more per hour. Agencies handle employee screening, supervision and paperwork, and charge for these services. This is a worthwhile investment for some people; others would rather save money and go the independent route. This article on hiring in-home care elaborates on this difference.
This is a rather long answer to a short question, but there isn't one simple response. Good luck nailing down the specifics you need.