Try the Gerber River shorty, which I own and like.

http://www.amazon.com/Gerber-05640-River...5692&sr=8-2

Or the Mcnett saturna dive knife, which i also own & like. I've never used the line cutter, but I don't think it weakens the blade.

http://www.amazon.com/McNett-Saturna-Blu...mp;sr=1-2-spell

They are both blunt tipped, and the saturna is plain on one side and serrated on the other. Blades are 3 inches long.

Both are low cost.