If you are in it just for a cheaper shave, then a coticule OR a norton 4000/8000 OR an equivalent is all you need to sharpen the razor.
The leather strop is needed before every shave.

Now, you MIGHT want to buy a pasted strop eventually, because a pasted strop can keep your razor shaveready much longer.
However, it is not a necessity, more of a convenience really.