Cost of Gas Central Heating

Does anyone have gas central heating and can give me an idea of how much it costs per month at this time of the year?

We recently moved into a new house with gas central heating and cooktop (not the hot water). We have just got the bill for the first month and it is $315 . We have been using it for an hour or so in the morning and then 3-4 hours in the evening. We did have a leak which has since been fixed which could have accounted for some extra cost, but DH did a meter reading this morning and in 4 days we have used 20 units which works out to over $250 for the month if we continue at that rate.    The power company originally estimated 35 units a month and we used over 150. Is it really that expensive to run??

Shellgirl - that sounds like a lot!! We cut the gas supply to our current house because of the horrendous daily 'for the pleasure of having it' rates! But our last student flat about 3 years ago was gas heating and water and that was about $150/month for 4 of us..

Thanks everyone for your replies.

We think we may have solved the problem. Turns out we were on the wrong plan and DH worked out the bill would have been about $180 if we were on the correct one. We also had a gas man come and look and there are a couple of holes in the ducts in the ceiling so we will have been using extra because of that as well. A bit of a relief as it is all stuff that can be fixed pretty quickly (especially seeing as how we are coming into winter at the moment).