I paid around $800 (at speakerexchange) for my second ND-1, the first one (a year earlier) was priced just over $600.
First one took several weeks to arrive. Second one came faster, but arrived DOA, and was replaced within a week.
There are now quite a few comments about using these in upgrades or DIYs - posted here and on AudioKarma (and elsewhere).
Google is your Friend.
Alobar has posted his REW results on AK (Below), and I got essentially the same, or good down to 23hz or so, with only minimal EQ (I simply used just one of the lower DIY M2 EQ settings (POS, thank you) for the ND variant).
https://audiokarma.org/forums/index....-again.835545/
(This is in a 5 cu.ft. cabinet).
NDs or ND-1s, for me: Brand New, Under Warranty, deeper, cleaner, really deep bass, significantly improved lower midrange (~1khz) and imaging vs. used, older, 2235s of unknown history/condition (so needing service to be certain) for (very roughly) the same cost....the NDs were a no-brainer, and
No Regrets!
That's my 2cents - but just enjoy the heck out of what ever route you take!