Several arborists internet sales places sell micro pulleys and line to make your own. Harbor Freight sells one called a Rope Hoist that is "rated" at 500 pounds for $7 (http://www.harborfreight.com/general...ist-45076.html
If you want one small that can handle higher loads the arborists supply places have the pulleys and rope. For instance at Baileysonline - one double pulley rated to handle 7,000 pounds and up to 1/2" rope is priced at $45. Two of those pulleys and your choice of rope, the length you would like to have, and you are set. Those pulleys are made by CMI and other places sell them as well. The challenge will be getting rope that is not to large, most arborists rope starts at 1/2 inch, with some down to 5/16".
Hope that helps