This will work for that length. https://www.amazon.com/TERNENCE-Com...sprefix=terence+chastity+,hpc,119&sr=1-3&th=1
I have purchased devices from DH Gate, they have good prices. I use only stainless - steel cages. The best so far is an inverted cage.
What’s “cheap” I found my every day one, it’s a cherry keeper, everyone has different ideas of what works for them, metal plastic ect. I think you need to get one you think will be close for cheap (Amazon ect) and when you find a fit that works then invest in one that you want to use for longer. I think I’m into my cherry keeper for around $100