From Fodor’s Travel Forum (you can find the discussion here):
I am looking for a travel insurance police that ONLY covers my airfare and apartment rental. I do not need nor do I want, medical, lost baggage and all the other stuff that most companies offer. I already know about comparison sites, and all the companies on their sites sell packages, not what I want. I know I might be out of luck, but it’s worth a try.
Unfortunately, travel insurance polices are designed as packages, and it isn’t possible to pick and choose the benefits you need and don’t. I know you mentioned comparison sites, and one option would be to visit one and generate a quote for cancellation. Then, select the cheapest policy that will offer the cancellation benefits you need. There will likely be other benefits included, but if you choose an inexpensive policy, they will likely be fairly nominal. This will help keep the premium low.