You can also dodge the "plus the $ for the bike rack"...
A friend bolted a big piece of marine ply to his racks (or vice versa), with numerous holes routed in, bikes go on upside down and ladder or ratchet straps (with their own holes in the ply) do the holding. Just make sure your engineering is well in order...
At least 3 bikes on board for less than the price of 1 bike holder, plus the bike rack doubles as a cargo holder - and the whole lot comes off in 1 piece = win.