that’s not even trying, you can get 5 in the back of a mondeo estate (seats up) with a bit of faff 🙂
OP : in my (ancient) mondeo estate, you can get 2 full size freeride bikes in the boot, with the luggage cover on. I’d imagine all estates of a similar size (vectra, accord, passat, etc) would be the same.
However, you will get more security with a saloon, and in a lot of them you can get a bike in (full) with both wheels on by folding down the rear seat (won’t be as secure but less hassle). If you don’t need the versatility of an estate but if you don’t need that, a saloon will be cheaper.
have a look at 5 series, volvo s80 (very cheap and comfy) etc