I wouldn't go diesel, just pick up something like a Octavia estate, the 1.8TFSi should give reasonable miles per gallon, certainly 45 on a run. I've had a Passat TDi 140ps as a hire car and that cracked 69mpg and was a very nice car, much more comfortable than the Cupra with plenty of space.
However you could do what i've done, I paid £800 for a 206 1.4, it gets over 40mpg and has a towbar, i then stick the bikes on the back of it. Having said that i'm getting the urge for a 500 Abarth, I could never go back to diesel.