So it began with $4400 dollars worth of tree removal to build greenhouse.  Not all for greenhouse but about 2K to be fair.  The rest were trees I did not want on top of my house.
Today the gas company came and to run a natural gas line to the back of my property which means over the bridge will be another 4-5K.  That was not part of the budget.  Oh well

If the gas line is already to your house, maybe a plumber or contractor would do the job of extending the line to your greenhouse for significantly less $$

Could you put a propane tank to supply the greenhouse?

I ran m y own gas line from gas meter to my garage. And gas company just hooked it to meter very easy. Buy pipe dope and pre threaded calvenized pipe and rent a ditch witch from home depot. Put pipe dope on threads use pipe wrenchs to tighten pipes thats it. Save a ton of money.

I talked to a man who looked into running a long gas line for a new water well.  The gas company told him if there was a leak along that line he would be responsible for the bill.  He chose to put in an electric well.

Can you setup your greenhouse to be solar heated?
 

Compost heats greenhouse:
http://www.farmshow.com/view_articles.php?a_id=93

Just use propane, it will be a lot simpler for you & probably cheaper than electric.  If you want to be extra safe, get one with a regulator where you can hook up two tanks & just switch when one goes dry (that way, if you lose track of how much you have used or fail to tighten the pigtail sufficiently, you'll have a fresh tank, ready to go).  For some reason, I was advised to use regular black iron pipe as opposed to galvanized for the piping -- not sure what the reasoning is but told not to use galvanized (but galvanized sure sounds better).

Someone mentioned solar.  You may want to take advantage of passive solar heating with some thermal mass to store heat.  Water is ideal for this -- it has a high specific heat so it will store heat produced during the day & slowly release it after sundown.  I know people who built plant benches on top of 55 gallon drums of water for this purpose.  That wouldn't be practical for figs but you may be able to work water in somehow for heat storage.

You should also make sure to invest in some type of temperature alarm if you run out of fuel or the heater fails for some other reason.

John

It's actually the property that is a bit of a problem.  The site is across a creek and the bridge really isn't meant for cars and trucks although the former owner drove across it the all the time.  Black iron is the piping of choice for gas.  My land backs to a park so can't in that way.  From what I hear for around here that is not a bad price but I will shop around.  I am checking but I think if they put it in then they are responsible for it.  The line will be about 200 feet and have to be attached to the bridge at one point.