Thunderwolf cavalry?

So what are ideas for Thunderwolf cavalry? There's no offical Games Workshop figure at the moment, so you have to make a plan. One way, but a bit expensive, is to use other wolf figures. Here's an example of a Circle of Orboros War Wolf (from Hordes) with a Space Wolf marine on top:

Not bad, but could work out costly. The figures are £5.85 each (for just the wolf).