Replaceable blade knives
The skill and time required to sharpen dulling knife blades is a trouble too much for most people nowadays. There is a wealth of very reasonably priced new and very sharp blades, most of which keep their edge well. A similar huge range of handles is available to take these blades and store a fresh supply. The increasingly popular snap-off blade can be allows up to a dozen new sharp points per strip. They are available in several sizes ~ the most popular are known as 18mm and also 9mm.
Heavy duty knives
Knives with 9mm snap-off blades
Knives with 18mm snap-off blades
A wide variety of manufactureres make these out of plastic ~ some have steel inserts around the blade ~ some are all metal. ~
Knives with 25mm snapoff blades
The largest snapoff bladed knife around ~ sharp and heavy

Trapezoidal sliding blade ~ plastic ~ by Stanley
$0

Scalpel handle ~ SM No3
$2.12

Pencil knife ~ plastic ~ five blades ~ coloured
$2.44

Pencil knife ~ metal ~ colours
$3

Trapezoidal sliding blade ~ metal ~ generic
$5