How much does nylon cost per gram?

Depends which nylon, and the spread is wide:

At the low end that is roughly double PLA. At the high end it is six times.

But the per-gram price is the least of it

A 200 g PA6 part at $50 a kilogram, printing for 9 hours on a 120 W enclosed machine, costs $16.11. The plastic is $10.00 of that. The 20% failure allowance is $3.22, which is more than the machine time and seventeen times the electricity.

A 20% scrap rate is not pessimistic for nylon. It is what happens when a spool has been out of a dry box, and the failure is not subtle: wet nylon prints with visible steam, foamed extrusion, weak layer bonds and a surface that looks chewed.

Drying is a running cost nobody quotes

PA6 needs 8 to 12 hours at 80 °C before printing, and needs to stay dry throughout the print, not merely start dry. Nylon absorbs moisture from the air faster than any other material on this site — a spool left out overnight in a humid room is measurably worse the next morning.

That means a dryer running alongside the printer, and a dry box feeding it. The energy is small. The discipline is not, and the cost of skipping it is the whole spool.

Where the money is actually justified

Nylon is bought for abrasion resistance, toughness and self-lubrication — living hinges, gears, bushings, tool jaws and anything that has to survive repeated impact without cracking. PA6-CF adds stiffness and dimensional stability and takes the heat deflection band to 120–190 °C.

If the part does not need one of those properties, the per-gram price is money spent on nothing. If it does, nothing cheaper will do the job.

One kilogram of PA6 at 1.14 g/cm³ gives 364.69 m of 1.75 mm filament, rather more than PLA's 335.28 m — a small consolation on an expensive spool.

Price a specific nylon part in the print cost calculator, and check the drying schedule on the PA6 material page.