I guess the least expensive place would depend on where you are located, USA, Canada or.
I ordered mine two years ago from the USA and by the time it got to me ( in Canada ) the price had almost tripled, so if you are in Canada be sure to ask about dutys,tax's ect...
But it is well worth it.
Picked mine up from Ebay, from a Place in Florida called CSE Offroad. The Best Synthetic rope made is from a company called Samson, and their AMsteel Blue series is the most common. You will find it about a Buck a foot for 3/16. You MUST also use a Hawse fairlead with rope, NOT a Roller Fairlead.