Cell-cups can easily be re-used, although they're cheap enough to buy in bulk.
Before the queen lays in a cup, the bees will 'polish' the cell cup - what this means is that they lay down a coating of a wax-propolis mix onto the cell-cup base to cover over the plastic (as bees hate plastic). While that wax is still fresh and relatively soft, it can easily be removed with a popsicle (lollipop) stick shaved-down to fit the cup - a quick rotary twist is all it takes to remove the lion's share of the wax - it doesn't need to be spotlessly clean, as it'll only get coated again next time.
If that wax is left (say, over winter) and turns hard, it can be softened by soaking in a Sodium Bicarbonate (Baking Soda) solution. This also helps to soften the wax which is attached to the outside of those cell cups which have been drawn-out into queen-cells - but it only softens it - it still needs physically removing.
So - if I need to re-use a cell, I first remove the wax on the inside with a popsicle stick, and then - using a length of blunt-ended dowel rod inserted into the cell-cup - push it firmly through a 10mm plumbing fitting (although anything similar with a 10mm hole will do the same job) which then strips-off any external wax.
All-in-all re-using them is a hassle, and it's much easier to buy-in a stock of cell-cups and use new cups each time. But - if you have time on your hands on a cold winter's evening and nothing else to do - they
can be re-used.
BTW - I found the Chinese cell-cups I bought to be poorly made. In particular, the rims were very rough indeed and needed to be wiped over a sheet of wet-and-dry abrasive paper. In contrast, the genuine Nicot cups are extremely good - so suggest you buy those if you can.
'best
LJ