They are expensive! Both the originals and repros are more than I wanted to pay. Another option are the marked stickers sold at sew classic.
http://shop.sew-classic.com/Adhesive...-PK-SCP001.htm

I got one from eBay and it didn't cost much. I sure love it!

Scotch is supposed to have some "reuseable strips for lightweight mounting" for under $4 that you could use to mark the quarter inch line - I am looking into where to find them - Staples maybe?

I have made a few purchases from April1930s.com and they have been great to deal with

By the way, you may notice the needleplates for the 221 are much more expensive than the needleplates for other machines; for example, Sew-Classic has the marked needleplate for the 15-91/201-2 for just $6, while the 221's marked needleplate costs $42.

Why? Because the needleplate for the 15-91/201-2 is just an engraved piece of metal, whereas the needleplate on the 221 contains the spring mechanism on its underside; more parts, thus higher cost.

Also, when you install a new needleplate on your 221, don't forget to ensure the bobbin case "finger" is positioned in between the two spring mechanisms on the underside of the needleplate. It's easy to overlook this and will lead to frustration; your machine won't stitch without that finger located between the springs.