Disclaimer:  I bought mine directly from the manufacturer in 1998
Shipping per barrel was pretty minor when we ordered 8 brand new ones.  The customary alternative, as noted elsewhere, is to purchase used ones from a local carbonated beverage dealer and wash out the syrup residue.
If you can do a group purchase of enough to justify the truck space (say, folks within a one hour drive of each other), I suspect the shipping cost per barrel will go down significantly.
I believe I bought ours from 
US Plastic in 1998.  Looking at the site today, I see that they run about $65 each, with a 15% discount for an order of 12 or more.  You'll have to call them to find out what that does for you shipping-wise.  IIRC, I paid around $30 - $35 each, not including shipping.
There are other (industrial) non-food liquids shipped in these that can be safely washed out and usually those drums go for nothing if you ask - they are glad to get rid of them.  Figuring out what is safe to wash/rinse out and what is best left alone is beyond the scope of any discussion here.  Personally, I don't bother - they get used for other non-potable uses.
HTH
Tom