I just checked and Sew Classic does have the best price on the Slant, clear, free motion and darning foot. It's on sale for $6.69. I didn't check their shipping cost.
Just so you know what to expect.....You have to wiggle and manuever it around some to get it on and lowering the needle all the way down makes it much easier to put the foot on. Secondly, you may notice some noise or clicking as you sew, but don't let that worry you.
Since the 301 has three thread guides prior to the needle, and that's really overkill, I have removed/eliminated the middle thread guide all together(just undo the little screw and it's easily removed). Then you don't have any problem with the arm of the FM foot rubbing & clicking. When you return to normal straight stitching it really isn't necessary to reinstall the middle thread guide; you don't need it.
If you're considering purchasing a new Slant walking foot.....I'll just share with you with you that not all of them work/fit on the 301. I have found that some fit the 401 and other slant machines well, but not the 301. However, I found a vintage walking foot that works very well on my 301's. Just say'in.