Tripcrown:
About $3,000 may be in range for a pond that size. $5,000 probably isn't even too far out of line. I've noticed that the contractor who did mine seems to bid around $5,000 for ponds around an acre in size and 10 feet deep.
Each location is different though. For instance, that the excavation filled up with that much water could be a cause for concern. If it has springs and the soil is too muddy, they may have to use an excavator (trackhoe) instead of a dozer or dirt scoop. They might have to dig the pond deeper than you desire and compact clay or install a liner. ** I have a question posted myself for the experts, but basically, as I understand it, if a spring exists in a pond that has enough pressure to bring water in, it can take water out as well if the pressure situation is reversed (water is heavy and if there is a lot of it above the spring, you have pressure...).
I have heard that the general guide is $1 per cubic yard in this area. A local municipality is paying around $4 per for excavation of silt in an old lake (partially due to prevailing wage requirements). My dam turned out to around 32 cents per I believe (I think my dam had around 43,000 cubic yards of dirt at a bid price of $14,000).
Even if you get a cheap quote, don't underestimate the total costs associated with the pond... My dam was bid at $14K and the contractor stuck with it even though I think he probably lost money, but I way underestimated the quality and amount of topsoil so didn't include it in the proposal. Removal of quite a bit of that at an hourly rate added about $7K. I have about $3K in the cost of lime, seed, etc. I'm using my trackhoe, my brother's 4-wheel drive tractor & dump truck, and a rented dirt scoop to build the four mini-dams to catch any sediment. The dirt scoop is at $100 per day and I have fuel costs for the trackhoe, tractor, and dump truck. Now, depending upon the weather forecast, I am considering having the contractor come back to help with two of the mini-dams. Then there is fish stocking (going through local NCRS office for most, but have $300 worth of fathead minnows already and plans to purchase some fish not available through them such as smallmouth bass and hybrid striped bass) and possibly a feeder / fish food. Then I found a "cheap" pontoon boat that I want to fix up to use also as a ferry to get mower out to my island and etc. My $14K pond may wind up costing closer to $30K. Should provide years of enjoyment and relaxation though... Overall, I think it probably added that much to the property values too.
I have a fairly large trackhoe and it still takes time to excavate a large area. You would need to dig down as deep as you want it, then move over, and keep repeating the process. It could be done, but would take a long time.
Good luck. Ponds are nice. Quick, relatively cheap vacations / therapy.