Friend had a .75 acre pond 18' max depth constructed for $8,500 last year I consulted on for him with local engineer. Pricing depends on many factors, but compared to this project, your quote obviously seems high.
One thing I would absolutely demand is proper compaction with sheepsfoot roller...add at least 18" clay on sides and entire basin in 6" lifts - compact layer then add another. Contractors for some reason around here are reluctant to employ this step - which baffles me. More time in the seat - cost of job increases along with their margins.
All the pond construction contractors I've met do not like being told their business...I consult with several local guys, and their initial responses were all the same. Now we've done some projects together, they understand - it's my customer's way or the highway. Mike Otto has taught us all well - do it right the first time, or double the original cost chasing leaks that may never be fixed.