Tried many ideas for a bike rack, but what always bugs me is safety, to make sure the bike would be well-attached at the back (and not flying in the car behind), and also having to remove it at night (having heard many stories of stolen bikes).
So, I looked for a not-too-expensive foldable bike, and received last week the Schwinn 20-inch Loop https://goo.gl/IWdMVi
for under $250 (shipping included).
Easy to setup, solid, lifetime warranty, and has lots of good reviews.
Comes with a carry-bag. So, now thinking on how to mount it on the roof.
And fun to ride