How much do you expect to pay for such a blade?

Based on retail price of the existing blades (50 x 100mm blades == 1 x 50m blade) puts it around $125. If they make them for ~25% of that, each blade is ~$30. Though I anticipate a higher cost to develop the process if necessary.

How many blades do you expect to purchase for a given period?

Around 50 blades per month for the first year

> (50 x 100mm blades == 1 x 50m blade)

You’re off by a factor of ten. 50m is 50,000mm, or 500 × 100mm.

I also would expect a very large price premium per unit length compared to the shorter blades, which must be made by the million.

Oops, thanks for the catch. That is just a typo though, so the following price is still correct (500 * $0.25 == $125). Retail price per blade is $0.20 - $0.25.

I've thought about the price premium and think it could go either way. The blades from at least one manufacturer are already produced from a single ribbon before being separated, so the process to produce longer blades shouldn't be too different (hopefully!). And if there's a 2x premium, that's fine, if its closer to 10x I would re-evaluate.