All figures approximate.
Butane heater:-
Cost to buy 100 Euros.
Gas bottle (exchange/refill) 15 Euros.
60 hours at 3Kw = 25c/hour
Paraffin heater:-
Cost to buy 200 Euros (plus).
20 litres paraffin 40 Euros.
48 hours at 3Kw = 80c/hour
Gas some water vapour, paraffin none.
I've no idea what the fuel costs would be of running a generator for heating but all forms of electrical heating are considered to be inefficient.
As for keeping the house warm, because of the construction of houses here (no cavity walls or insulation), any heat gathered during the day/evening will be lost overnight.