New tree surgeon harnesses can be very expensive typically £150~£200 and at least £50 for a used one. For small and occasional DIY jobs a cheaper alternative I use is to make a harness out of car straps by copying the basic design setting of the expensive ones. The straps can then be reused for their original purpose.
Keep in mind that what follows is not the best possible solution and you do this at your own risk. I decline any responsibility of any harm or injury or damaged caused by the use of such method.
make loops on the straps (straps like http://www.s2as.com/p-Dakine_Tie_Down_Straps_12_2011-3973.aspx) as indicated, (position depend on body and legs size) the loops are needed later to keep the lateral downward ones (wihout loops) in position. one strap with 2 loops, 2 straps with one each , 2 strap with no loops, length at least 2 .5 metres