I purchased a pack of ten replacement blades, for a utility knife, at Harbor Freight for $2.98. I then wrap the top with two layers of duct tape, in Bronco orange of course, and it makes the best seam ripper I have found.
These should not be left laying around where there are small children, but then that applies to many of the tools used in quilting.
Just a suggestion, after spending lots of money on the "ultimate" seam ripper more times than I can count this works the best for me.