Ok. I have personal experience in this realm. If I don't post what you're looking for, just ask.
I have a 1/2 wine/whiskey barrel. It was $23 from Lowes. It's not water-logged and I didn't feel like doing it so I went with a liner, also from Lowes. We actually got a packaged deal which included a faux hand pump water feature and a small pump. It was another $20. The barrel (full is 55 gallons) is roughly 25 gallons filled. It took 4 full 5
gal buckets and about 3/4 of another to fill to my desired line. I used to have a Penguin100 filter on it, and that cost about $15. I bought gravel substrate (not nearly enough, but it's a work in progress), a water iris, anacharis, and a Majesty palm (shade from the outside). If you're expecting full light, you'll need more plants. Luckily, I have a friend with a full Koi pond and she gave me a potted hardy water lily. Oh, I also picked up a 100W heater for $10 or so.
So anyway, my total initial cost was about $80. Of course, I've had to buy other items since then. It's really no more expensive than an aqurium. In fact, it could be cheaper, depending on what you do. As for the dog, however, he will EASILY be able to reach the water. It's only between 18" and 24" tall for most cut barrels. A 3/4 or full would be tall enough, but too deep for easy maintenence I believe.
Here's a shot of mine. Still a work in progress. I have to reset it every year since I don't winter it here in New Mexico.
