This instructable covers the steps for a very cheap and in my case a rather crude Kindle Fire cover. Some of my pictures didn't turn out well "but" by looking at the results I hope you can easily see what I did. If not, ask questions.
A book of questionable value equal to or larger than 9-1/2" X 6" X 7/8" thick. The dimensions of the book are so you will have ~ 1/2" clearance around your Kindle inside the cover. I paid $1.00 for mine at a thrift store. -OR- something nice like a Moleskin notebook with a strap to hold it closed. Your choice.
Three sheets of dense foam from a craft store. I got mine from Michaels @ $.99 each. If you want to be really frugal you can get by with one.
Two thin hair bands. I took two from a card full I bought for a $1.00 I have in my car for my girlfriend who never seems to have one when she wants to put her hair up. You might have a couple just lying around or someone willing to donate to the project.
A strip of duct or similar tape.
Some cardboard about the size of the Kindle for a template.
If you want a strap, about 4" of Velcro strap.
A carton cutter or similar.
Something to measure with and if necessary you can just wing it using your Kindel to get your cuts close enough.
Of course use caution with the blade. Any blade can injure and stitches or worse aren't fun. Don't bother asking how I know.