I found this supplier while looking for aluminum rings to use on tree huggers. They warranty the rings to 250 lbs but they say a single ring will lift 3000 lbs. Maybe someone has the ability to do some testing on them but if they work, they are sold in pairs so at $3.30 / pr compared to around $3 for a single.

http://slingrings.com/sunshop/index....=4&prevstart=0