I build custom tanks on the side. Some of you may be familliar with my DIY threads. I recently built a 105gal acrylic for a customer, and the materials alone were $900 (2x 4x8 sheets of 1/2 acrylic plus taxes, cement, applicators, sandpaper, novus polish.) This is obviously not very cost effective, but he wanted a specific size and he could afford to pay for custom work.
Around 200-300gal is around where DIY becomes more cost effective for acrylic, but then part of that is because it's not easy to find a manufactured 300gal that doesn't need to be shipped.
All glass is even worse for the DIYer to try to get cheap, unless you find it used, or know a glass guy or something. Buying the glass to built yourself a 100ish gallon tank will cost way more than just buying a tank off the shelf. Again the tradeoff point comes in around 300gal, depending on the dims.
Plywood is **** cheap, and glass for plywood builds can be salvaged from used tanks. Even if you get the window new, you're only making the important side clear, and the rest of the tank comes cheap. What I find unfortunately (and this is just a function of my personality) is that I have ideas as I go for how to make the build cool or sexy or just plain sweet, and generally these ideas aren't all that cheap. Things like laminating the bottom of the tank with fiberglass to resist damage from rocks and decor, or using expensive tooling gelcoat because it's stronger, or using aluminum flashing on all the corners to cover screw holes and dress up the tank. My 180gal build cost me around $1500 by the time I was done with the oak front, 15mm glass, and all the equipment to run the tank, whereas it could have been done for around $400. My 600gal build is so far struggling to stay on budget, because I keep having these wonderful ideas...
