Wow, 7 lb - that's amazing!
I'm thinking close to maybe a half pound saved between tuners, wood knobs and maybe the bridge being a smidge lighter?
Did you chamber the body, or is the burl top much lighter than a typical hardwood top of the same thickness?
Wood knobs maybe a couple ounces saved. Tuners a couple ounces. The neck is fairly slim and maple is less dense than a lot of other neck woods (much less than ovangkol, at least). The walnut body is not chambered (other than the huge control cavity) but it's pretty light, and this is a pretty compact body shape - probably smaller in real life than it looks in photos. Plus it's only 1 3/8" thick in the body. With my other bass, I really think it's mostly the bubinga and ovangkol, plus it has one of those old school multi piece warwick bridges in solid brass, so it's a very heavy bridge.
The burl itself was probably extremely light, but it's soaked in epoxy so it's definitely not light any more!
I'm fairly interested in what you actually have into it (not counting your time, but a total of hours would also be interesting too) vs what you'll list it for. I know, that's asking for a magician to reveal his tricks.
If I knew the exact answers to those questions I would definitely share them. I don't though and it might be hard to guess, especially for something like this where it's a smidge of this piece of wood and a bit of that piece of brass and the neck blank is basically glued up leftover strips from a guitar I built last year, and so on. And an hour or so a couple times a week in the early morning, plus an occasional few hours on a weekend, stretched over two months. Going from raw wood (versus prepared Luthier Wood) and making my own hardware and electronics definitely reduces materials cost - this is probably about the cheapest way to build a bass like this. But there's a huge trade off in time.
I would think of it this way. It takes 5 minutes to order a $200 set of Bartolinis or Delanos or whatever. Job done. You have pickups to put in your bass. You know they're going to sound great, and people will recognize the brand name. No drama. It helps to know what sound you're after but it's pretty hard to go way off the rails doing this.
Or you can learn to make guitar pickups, build a couple iterations of a pickup winder, decide you also want to make bass pickups, then unlearn half the things you thought you knew from making guitar pickups since it turns out it's crap and people building bass pickups are more focused on the truth than tradition. Now, spend all your free time casually browsing the internet trying to find suppliers selling things appropriate for making bass pickups (hint: there aren't many out there, 99% of pickup making is aimed at copying famous designs). Then, re-learn CAD after not touching it for 20 years so you can send your designs off to get laser cut flatwork since you're interested in building something besides another P or J pickup. Next, build enough different bass pickup designs that you get a rudimentary understanding of how tone actually works in a bass. Finally, narrow in on a specific design that you like the best for this particular bass, and build at least half a dozen iterations of it so you can fine tune things. I do sell a few pickups here and there, and use them in my own instruments, but the bulk of the time I spend winding coils and assembling pickups is spent developing, not making a complete product. I would bet hard money that at least 3/4ths of the coils I've wound have ended up in the trash, in the name of constant improvement.
Phew. Catch your breath.
All that, to get to the point where instead of spending 5 minutes ordering a $200 set of pickups, you can spend two or three hours turning $15 of materials into your own pickups! There is no way in heck that makes even any sort of remote sense from a financial standpoint. The good news (for me at least) is that it's way more fun!
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