Funny you mention pool costs! That is how I slipped our pond through the budget committee.

We went and priced out a simple above-ground swimming pool, not even that big, that was of reasonable depth (I forget the actual size). By itself, it was affordable. Then I had to figure in leveling an area for it, adding sand, and adding the state requirement of a deck to support a locking gate or removable stairs, a motion alarm, etc. Also chemicals, electrical hookup, electricity costs... my nanny state of NY made a simple pool cost almost 3X of the base price! Grand total, $11K.

We first received a pond quote for 1 acre pond at $10K, so we knocked it down to a 1/2 acre at $6K (which wound up being ~$9K when complete). It was still less money than a pool so I got the go-ahead! The selling point is it is usable all year round, where a pool is only good for 3-4 months around here. Ice-skate, fishing, etc.

Now we may have to add the cost of aeration and associated electricity to keep the floating gunk at bay for swimming. We will see how this summer pans out.

Don't skimp on the build of the pond. You will pay the additional cost now, or more later.