So you’re selling domain names that you don’t own and that anyone can register themselves?
Yes.
How can you justify charging ~$650 for something that someone can do themselves on most domain registrar sites?
Creativity is valuable. I'm charging for the name you didn't think of.
25 Domains for $650 comes out to about $26 per domain. For a 5-6 Character domain of extremely high-quality and related to Bitcoin I would imagine you'd be paying a lot more than $25, or even $650. My justification is that I could easily purchase the domains and flip them individually, and people purchase worse domains at much higher prices everyday. I do not have the time to do that for all of my domains. There are thousands of unclaimed domains just sitting here in my list.