Custom made or from the shop?

It depends on what size you want. It will usually cost just as much if not more untill you get into 200+ gallon tanks.
 
I would say the classifieds. As long as you can verify it is sealed before purchase or make an agreement to return it if not.

IMO I would only get a custom tank if I want a custom acrylic or a drilled tank for a sump.
 
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