So a few years ago I was getting ready to move and packed up my single cup coffee maker. I really wanted to make some coffee (the stuff at the coffee shops is just too expensive!) so I figured out a way to do it without buying a coffee maker. I used a red plastic bowl and knifed slits in the bottom to hold the coffee and filter and I've been using it ever since. I have a dedicated pan for boiling water so it only needs to be cleaned once in awhile. It's just so much easier. You can't set a timer, but I don't miss it. It's finally starting to break apart so I thought I'd build a design to print out that would replace it and also fix some downfalls of the original (mainly just somewhat slow drainage).
The only issue is what material to use for it. I would recommend using one of taulman's materials that can withstand the heat and is FDA approved (the 618 isn't approved, but I have it and it states it is inert to the body so that's what I'm going to try. Use at your own risk if you use that material. I would not recommend ABS).

Update: Printed out and coffee tastes great! I put the strainer in a pot of boiling water and it didn't lose structural integrity.

Update: Added strainer for smaller diameter cups

Coffee_strainer - original with curved bottom
Coffee_strainer-2 - original with flat bottom
Coffee_strainer-smaller_cup - modified for smaller diameter cups.
I would recommend using one of taulman's materials that can withstand the heat and is FDA approved (the 618 isn't approved, but I have it and it states it is inert to the body so that's what I'm going to try. Use at your own risk if you use that material. I would not recommend ABS).
This design does require supports except for the bottom and first "step".
If you print the strainer for the smaller diameter cup, make sure infill isn't 100% as there are some thicker portions due to the curvature of the part. I would recommend 20% w/ 2mm thickness. That's just generally what I've found to work good.