Big picture, starting at around $5,200 +. Variables include access, depth of pond, length of stream, type of stone, fish/plant package, landscaping around pond, etc. If just the pond, 3 shelves, 24" deep max., waterfall set on or w/in 2' of the edge of pond, just mulch around, & minimal retentive stone work around edges/backside of falls, then in that $5,200-$5,500 range, again assuming good to decent access. This would be an Aquascapes kit w/a 2000-4000 GPH variable remote pump. Hope this helps.
Ponds are a lot of work if you're going to build them functional AND natural looking. If you fail at one of these, it will be the worst money your Client ever spent. If you succeed at both of these AND you make money, they'll regret not having a water feature built sooner!