Fuel consumption is always important, but you need to think of what your driving is mostly going to be like.
If you drive mostly in town, a 1.1 econobox is going to be far cheaper to run than a 6L v8.  On the other hand, if most of your driving is motorways then something around 1.8-2L is going to (typically) drink less because it'll rev less at higher speeds.  Depending on the make of engine, obviously.
And I don't know what Sweden is like, but a taxi or hire car here in the UK will cost hundreds of times what a bought car would.  When I used to get taxis with the shopping (which was about a 15 minute walk from my house) it'd cost me £5.  No way my car would use £5 worth of fuel to cover the same distance.  And a hire car at even £50 per day is going to eat money faster too.  My trains to rehearsals totalled about £15 to get me to and from rehearsals every Sunday (about a 70 mile round trip).  £15 in petrol will do the same journey a handful of times.
Maybe once you take maintenance into account the figures start to catch up, but I still reckon surviving on taxis and hire cars is vastly more expensive than owning a cheap runaround.