Morning folks!
Dodraugen, first find out whether the meter is only for your flat's consumption of gas. (Some landlords partition a flat into smaller independant units, but leave the meter in one unit - not saying that your landlord did this, but just confirm).
From the very light usage that you described in your first post, I would say $120 sounds about right. Gas consumption will go up in the winter months because of hot water showers, but I would say not more than $200 in your case. (You don't seem to do a lot of cooking, etc)
Try offering $150 for a start and take it from there...