The only way to know for sure is to lay out a similar system on paper with similar features and compare it. Be sure you're not comparing it with the cheapest components available as that system has low iron glass, good pumps etc.
You will be able to come up with a box of 650 liters of water for less by shopping used or using bargain components, building a stand out of lumber, etc. The question becomes a comparison of the mistakes you'll avoid, physical appearance, ease of use etc etc.
One thing about buying a quality AIO: You'll avoid many mistakes. For example my RS AIO never ever has a leak or shows salt creep. Some DIY systems I've seen didn't get this right and they're a mess that I could never put in my living room.
But on the other hand, a skilled & experienced builder can indeed some up with 650 liters of fantastic tank, probably for a little less money. But the difference may surprise you.
When I started out, oddly enough, no LFS was capable of doing this for me. They talked a good game but had nothing in stock for me to see & evaluate. No written quotes. Very confusing. I did not have the skills to order individual components, find big tank builders and all that.
Well, that's my perspective. Good luck with whatever way you go.
