You'd be surprised how close they can be in price depending on what tank maker you go with. I would wager an Innovative Marine 60" aquarium would be in the $2800-3000 range. Custom might be slightly more and this would mostly be related to shipping costs and the stand as custom 80/20 stands are more costly when they are custom.
This 60" x 30" x 17" aquarium from Miracles Aquariums set me back $3400 Canadian or roughly $2650 US. And about $700ish of that was extra expense due to me changing up the Dimensions after the glass had been cut. Stand, well I built it myself from 3/4" Plywood and laminated pine trim cost me about $500 CAD including paint and stain.
Still in the process of getting it up and running but you get the Idea. I'd be willing to bet the same tank now would set you back about $2200 USD plus whatever the stand costs. (Just an estimate as things might have changed with glass availability and other things).
Don't forget this is a 100% custom option so you get EXACTLY what you want, eurobrace, no eurobrace, the right height and width for you. Whatever overflow you want etc etc. Why settle for whatever dimensions a mass manufacturer decides is best for them to make? Or wait for what "Could" be years, if ever?
Just food for thought...