I remixed Qjr's no. 4 scalpel handle to work a little better for me. Here is the version that should fit the more popular size 3 scalpel blades. Still surprisingly durable and flexible in PETG.
I printed these at 100% infill, 0.1mm layer, 0.4mm nozzle. The trusswork is 0.5mm wall.
Cura will slice this correctly.
I added a few more edits to this version so the blade slid on nicely. I needed light pressure with pliers to get the blade to fully snap in, but I don't want to make it any looser. The sliding friction is more of a problem with this size 3 version. Please note, these are not sterile and can break. Be careful not to cut yourself when installing/using/replacing and I wouldn't recommend printing with PLA or any weak materials.
Also available: Scalpel Truss Handle - Size 4