I think you need to factor in a few other points not just the price of the colour coat!
CND Shellac only ever requires 2 coats of colour with beautiful opacity even with black! Saves you money not having to apply 3/4 coats.
CND Shellac requires PEP no removal of surface shine, saves you the cost of the nail file.
CND Shellac doesn't require a primer or 'dry brushing' again saving you the money of those two products.
When removing CND Shellac you don't need to 'break the seal' therefore using less time and again saving the cost of a file.
And my favourite thing about CND Shellac is the time it takes to removed!! Anyone that has tried it compared to another product will know what a breeze it is to remove! This saves you a lot of time! And time costs money
Again don't feel you have to throw something away you can use the systems along side each other then just don't replenish the other range when it runs out! Just remember to use the full system for both products don't mix and match!