Is there a point where it would be cheaper to build your own tank instead of buying. I want to build my own 300 gallon tank, but I hesitant to even start because 1. I'm lazy 2. I'm not sure if it is cost effective. If there is a point where its cheaper to build your own tank instead of buying what tank size would that be?
IMO, the most cost effective way is to be patient and flexible and watch the used market.
Watch ebay and Craigslist and the message boards of your local fish clubs, etc..
Honestly, even though gas is expensive now, spending a day driving to get a tank is really more expensive than spending all the time to DIY a tank.
As an example, I got a 300 gal acrylic with built in sump, stand, and a ton of extras for $1000.
Just make sure you see the tank filled with water and not leaking before you buy (especially on a glass tank).
If you are flexible on dimensions/gallons .. you can get a great deal on the used market.
Someday, I want to DIY a tank just for the fun of it. No time now though. And I would want a DIY tank in the basement, because I'd never completely trust myself that it was done right.