Ours fits inside my 406 estate wheels off – can actually get it in with only 1/3 of the rear seat folded if I take out the rear seatpost (convinced with a bit of effort I could fit 2 in like that, along with 4 riders). If you have a smaller car there’s always the option of fitting it through the back into the front seat (like I do with a windsurfer) and your passenger sitting in the back seat (in tandem!)
Alternatively, before I bought this car I used to carry it on the roof using an axle fitted through the end of my kayak V bars (basically a long bit of square section alu with V shaped cradles on the ends) in just the same way as a standard front wheel out carrier. Rear wheel tied down to the V bar. If you want a roof carrier, getting a bit of square section alu like this and making your own has to be cheapest.
To help those having trouble visualising a V bar, here’s a pic of a kayak on one: