Goldfish ponds are only as much work as you want to put into them. If you look through the Better Home and Garden magezine and say "Oh, I want that one" and you expect to see the bottom of the pond and all it's inhabitants, then you are in for a lot of work. We have a large square koi pond the father in law built, just bought the liner and dug a hole. We don't put much maintenance into it, we've only recently restocked it thanks in part to a great blue heron who deemed it a free Japanese sushi buffet.
Unless you have ducks and they get into it and muck it up, many ponds don't need a filter. So the whole cleaning a filter thing is overrated, but if you have a filter, BEWARE! You'll be cleaning that sucker every day.
The only maintenance most goldfish ponds need is the occasionally filling with a water hose and the raking out of leaves. Save your money, don't buy Koi, stick with feeder goldfish. Cheaper to replace. Provide things like sunken plant pots and such to provide the fish a place to hide when the cats and such show up. The smart fish will get away.
-Kim