I wouldn't know about the discreet part, I've always used clothing to solve that.

But for the "cute" designs on plain diapers, here's a cheap fix (If you have access to a printer):
1. Purchase some
8x11 sticker paper for printing a design on
2.Go online, and search for baby wallpaper or patterns save the image file of some you like.
NOTE: Save to a secret spot, Wipe your browse history, and erase the "My recent files" link after for privacy!
3. In Word, with the paper in a vertical layout, position the the image you saved so you can get
3 prints for 3 diapers. Print out and use a scissors to cut the paper into 3 individual stickers.
This method gives you tape-on designs for your diapers that will work, without a bambinos price. $36 for the paper sounds harsh but remember you get 3 prints on each piece...so that's 300 diapers

Hope that helps