home mining is tough right now. depending on your region and how much they charge for power. you may be better off buying the coin instead.
This is true. Generally speaking the prices that mining manufacturers are charging for retail customers are higher then what can realistically be earned from mining (even before subtracting the cost of electricity). In order to be able to realistically ROI on physical miners you will generally need to buy at the very least tens of thousands of dollars worth of equipment, much more then the OP is considering purchasing.
Yet they sell hundreds of hardware each new generation.
What discount can you get if you buy 10 or 20 in bulk? 20%? Is it enough to ROI? Not always
It depends but 10 or 20 most likely will not get you 20 percent. Even 20 units is a drop i the bucket to any of the manufactures.