let say you are mining monero with 50 gpu in 7 rigs , rx480-8GB cards with modded bios optimized for xmr mining , you purchased those cards a year ago when you was bale to buy for 250$ or less
If you are trying to jump into the mining business now , then ur ROI is definitely going to me much longer than a year ago

i would love that 2500$ "crumbs" every months  

50 cards - 2529$/months
10 cards - 252$/months
1 card - 25$/months

and the result is with today difficulty (September - 05 - 2017 )