I picked up a couple DIY kits from Cabelas a few years back and had my daughter help me mold them. Came out pretty good but the 2nd set will be inserted farther into my ear canal for better holding. Cost me less than $20 I think. Foams ear plugs are fine for short rides and are better than nothing. Plus they are cheap but you may need to change them out after several uses as the effectiveness diminishes. I've found that on multiple days riding that the foam plugs tend to irritate the skin and will actually wear off the outer skin leaving it raw.
Interesting take on the foam plugs. When I used to work at the plant, they were in for 8 hours a day, every day, pretty much all day long (except for breaks, lunch, etc) and I never had any kind of irritation issue like that. Hmm.....
And as for Noise Reduction Ratio, I've never seen a rating on custom molded plugs, but the little foam jobbies had a better rating (and, indeed, performed better) than any number of the 'industrial' alternatives (muffs, plugs, etc).
But, as you say, any protection is better than nothing, because one will surely suffer hearing damage otherwise.