I wouldn't buy an nc24 at any price.
Exhaust collector boxes rot and disintegrate if removed (if not already fked before you touch it) and even if you can find one in stainless it will be £200+. That's if you can find one, you probably won't. Even if you do you will have a pig of a time fitting it.
Add to that skinny forks (sure you could change them) and odd tyre sizes, but the rear swing arm which you can't easily change restricts you to about a 130 or maybe 140 tyre max. The frame is spindly and flexible.
And it has the traditional Honda charging woes, especially now as it's so old.
All that said, the motor is a peach and if it has a stainless exhaust and is really cheap you might as well at least have a look. But in the end if you specifically want a v4 400, save up for an nc30. If you're not fussed about that (admittedly very special) engine configuration and cam gear noise, then just get a 500 twin which will have very similar performance, or a 600/4. You can do a lot with an early cbr600, the frames are old fashioned but look good naked.
Oh yeh, the nc24 frame is hard to do well naked due to how the frame joins the rear subframe. Not pretty and not easy to do prettily.