It's well more than 256,000. You'd need over 300,000 Lums to get a Zod.
Figure it like this (I am leaving out the gems from the recipes because they're easy to get):
You need 2 Chams to get a Zod.
For 2 Chams, you need 4 Jahs (2 Jahs = 1 Cham. Thus, 4 Jahs = 2 Chams = 1 Zod).
For 4 Jahs, you need 8 Bers (2 Bers = 1 Jah. Thus 8 Bers = 4 Jahs = 2 Chams = 1 Zod).
For 8 Bers, you need 16 Surs (2 Surs = 1 Ber... you can do the rest of the math)
For 16 Surs, you need 32 Los (2 Lo's = 1 Sur)
For 32 Lo's, you need 64 Ohms
For 64 Ohms, you need 128 Vexs
For 128 Vexs, you need 256 Guls
For 256 Guls you need 512 Ists
for 512 Ists you need 1024 Mals
For 1024 Mals you need 2048 Ums
For 2048 Ums you need 4096 Puls
For 4096 Puls you need 12,288 Lems (this is where it gets more expensive, as you need THREE of the lower rune to make the higher one. So we start multiplying by 3)
For 12,288 Lems you need 36,864 Fals
For 36,864 Fals, you need 110,592 Ko's
For 110,592 Ko's, you need 331,776 Lums
For 331,776 Lums you need 995,328 Io's
For 995,328 Ios, you need 2,985,984 Hels
For 2,985,984 Hels, you need 8,957,952 Dols
And I think there are 14 more runes below that. So multiply 9 million by 3 14 more times. It easily surpases the billions.
The number of El's you'd need to Cube up to a Zod is:
4.28456E+13, or
42,845,600,000,000
Or, around 43 trillion El's. You'd better get started on those Countess runs now.
EDIT: Correction, I think there are only 13 more runes below Dol. That would still be 14.3 Trillion El's.