I haven't seen anyone build a 800D clone. First, there are a solid 5% of DIYers that can build a speaker with the class of sound the 800D provides (I admit I am a fan boy of the B&W D sound). Further there are maybe .1% of serious woodworkers that could approach a visual/performance clone of the 800D cabs. Maybe 1% of professional woodworkers could do it without a solid set of plans. That is because there is a WHOLE lot more to the 800 cabs than just woodworking. It would be a very skilled human or one willing to seek out and line the pockets of those who have the skills to approach a 800D clone. Even with the proper skill sets $2,500 seems like a non-starter even if one did all the work themselves and didn't consider their time worth anything. Now this isn't to say there aren't some proven designs with much more conventional cabinets that would be in the ball park of subjective and objective performance in the 5-6K range assuming one could build their own cabs.
Just a for instance (not saying this is the best value by far) but the Klang-Ton Nada is a small 2 way monitor that gets a lot of positive praise in the more high-end (price) oriented DIY community in Europe (we tend to be more budget oriented here in NA). The Nada has a "mere" beryllium tweeter and parts alone are in the 2K range without beginning to max out the last Nth degree of tranparency in the crossover components.
I will go out on a limb and say it will be hard to reproduce the B&W sound at 93dB sensitivity as Tuxedo suggests, well without bespoke drivers. The drivers on the market that one would normally go to for a B&W type presentation are going to be low sensitivity "audiophile" speakers.
My guess the guinea pig who makes a solid 800D clone both in voice and aethetics will be out of pocket 10 grand or more. I have yet to here a non-diamond tweeter sound like a diamond and the Accuton D20-6 is going to run you near $6k for a pair or the Jantzen 1024 for about 4K... Not sure if B&W will sell rare drivers to anyone but an owner but the 8 drivers (with the tweeter encolsure) run just under 5K. Iirc the Xovers are about 1k. I am not saying there aren't DIY designs that you may not like as much or better than the 800D for well under $10K but you are likely to have far different ears than I do if you can find one for 2.5K in parts.