Any reason it has to be a 26" frame? Wouldn't a 29er frame be easier.
I already have a rigid 445mm fork I'd like to build this around and wouldn't mind the shorter wheelbase of a 26" bike and I think they are more flickable. I have run a few of my 26" hardtails with 700x28 and 700x32 tires for years and love 'em.
The only 29ers that I know would work with this 445mm fork would be the early Raliegh XXIX (heavy frame) or an OS Blackbuck (not cheap).
Besides, I figured a used 26" hardtail are less desirable and hence "should" be cheaper than a 29er.