Here it cost about $2.80 a lb to buy it strait from the gas suppliers. They don't want to sell direct or to most people. They will not fill small bottles. Only 55lb bottles. I have a HVAC business, have all licensing, etc.. to buy from and have accounts from gas supplies. For some reason it is a huge pain in the ass to buy direct here. I only found one place that will sell directly to me industrial nitrous. I have a buddy that has two 55lb bottles sitting at his house that he said I can use. The supplier says that they have too many problems with people buying nitrous and trying to filter out the sulpher and using it for illegal purposes. Says they only sell nitrous in their bottles and I have to rent them. Cost like either $10 a month or $90 a year to rent the bottle. Their is one place in town that sell nitrous for $4.50 a lb and every one else is $9 to $12 a lb. I don't use nitrous a whole lot and only use like 10lbs a month. I get a 10lb bottle filled and use it to fill my two 2.5lb bottles at the track. I have a $150 very accurate to the 1/4oz scale and know how to properly fill a bottle. I thought I could fill the 55lb bottle and sell it for like $7 a lb filling bottles for people at the track. That didn't work out so well.... Most are cheap asses and complain that the one place is $4.50 a lb and think I should sell it for $4.50 a lb. The $4.50 a lb place is open mon-fri 9-5. they will take time off work and drive 10-20 miles each way to fill one 2.5lb bottle and if they can't do that they will drive 20 miles to the one orielly that sells nitrous for $10 a lb late nights and weekends. then complain that they had to do that, can't use nitrous that weekend because they didn't have time or couldn't go get their bottle filled, can only make a few passes because they only have one bottle, they didn't fill their bottle all the way, etc...
So I just get my 10lb bottle filled and gladly pay $4.50 a lb. Not worth the hassle to me to save a couple $ trying to get my own 55lb bottles and try to sell it. If some one was always at the track and I could rely on them filling my bottles for me I would gladly pay them $7 a lb so I don't have to go out of my way to fill my 10lber.
Sorry for the long rant. Most of the time the person filling that bottle does it to make a living. How long does it take to properly fill and weigh a bottle, bleed the line, lose nitrous bleeding the line, etc.. Got to make it worth their time. What would you charge?