need an idea for a new cage

Hey everyone sorry i know you haven't heard from me in a few weeks been really busy...any ways, i'm thinking of making a new cage for MOlly and Zombina. their cage now just fits two rats but its made for ferrets not that great quality and doesn't leave much room to work with toy wise. Besides i need a bigger cage for them now that summer's here my work is having me work way more hours than a part timer should so i need my girls to have alot of space to get excercise and run around when i can't play with them. plus the need space for when Zombina decides to be a bi......be mean so i can seperate them with out recaging one of them. I was thinking of making a grotto but i don't know how hard those are to clean. i need to stay with in 100 dollars or below for this project and work time not too exceding maby like a weekend project legnth or something. any ideas or plans premade would be incredibly helpful.

PS i have alot of ideas for them i would like to add in here like a small swimming pea dunking hole and a bottom layer for digging so if you could help me find a way to incorperate those into the plans would be amazing

Thanks in advance
Mark