Let's see. Two styrofoam coolers were like $3 each. Box cutter was $1. Quart of drylok was $12. I got two colors of tint at $5 each. And a tube of aquarium sealant to glue it in was $5. So $34. You could go cheaper if you just used styrofoam scavenged from packing materials or something. And you could get by with one color of tint.
It took me maybe 2 hours of actual labor, but I did three coats of drylok which I let dry for 24 hours in between and then let the whole thing cure for 72 hours before filling up the tank.
No problem. I really like the way it turned out. There are some super creative ones if you look on google. Looking back I would have made mine taller because I hadn't picked out plants yet, and most of it is obscured by the plant jungle now. But I built in a bunch of little ledges for plants which worked out great because I got a few plants that need pretty high light to grow, so this way I can have them a good 12 inches closer to the source of light.
Mine is a 54 gallon corner tank. You would probably need a gallon of drylok instead of a quart and more styrofoam. Probably more silicone too. You can get sheets of Styrofoam at home depot for under $10 for a pack.