Granted, not everybody has the same skill level, but here is an example of a stand I built for my daughter for her bearded dragon. This stand is built entirely out of generic pine 2x4's and wood glue - no nails, no screws other than hinge/slide hardware and also some 1/4" finish sanded plywood for the door centers. This stand would have no problem supporting the weight of the 40g breeder tank if filled with water.
And this is a stand I built for my other daughter. This one is almost entirely oak.
The interesting thing about the oak stand is if you look closely, the 4 bottom cabinets are actually kitchen wall cabinets I got from Menards for about $25 each. They came with an oak face, hinges and the door - super easy start. I added 1/4" oak sides where exposed, then added all the various oak trim to create the finish product.
Now, for you project you could look around and see if there is a 30" long kitchen wall cabinet - might be cheaper in the long run. Or, use the pine 2x2's for the corners. Add some 1/2" OSB board (not very pretty, but still pretty solid) to the back and sides. Then get some 1/4" oak veneered plywood (actually pretty cheap) to cover the OSB. Design/build the stand so the outside dimension of the OSB matches your tank. When you add the 1/4" oak sides, make them just a little taller so the tank can't be pushed sideways (not that it really ever would move with water in it, just the way I do things). Now, for the front you can use the same 1/2" OSB. Cut out your door openings to match some pre-manufactured oak doors from Menards (or your favorite store). Cover the front OSB with the 1/4" oak, then install the doors. If you want to finish the stand a little more, you can add 2 oak corner pieces (they look like an L) on the outer edges to cover up the 1/4" oak joints - look at the pics above and you see what I mean. Depending on what you pay for the doors, you could likely build the above for $60-$80.