ok lets say around $ 18,550 thats probably on the low side landscape center just put one in down the road from me about the same size for $14,000 . 35 ft x 16 2 falls 30ft stream with bridge. The guy said he had $3000 in materail not a bad profit that was the pond only. I would like to do a few of those
for $20,000 you could maybe get the supplies, but very little labor.
After proper filtration for koi, pumps for streams and falls, lighting, mulch, rock, liner, lumber for decking, and cheap labor $48,000.
I did a 23' x 16' with a average depth of 66", Upper pond 10' x 5', 40' stream split into two cascading fall, with no lights but some extra patio and landscape work, my cost for materials was over $20,000. Pumps alone were $1,000. I hope nobody here is installing something like this for $6,000. Building ponds is fun, but paying your customer to let you build them one, takes all the fun out of it.