Good but Cheap Treatments for Flutter Echo

I have a small listening room (11x12). With careful placement, Roomlenses, and velvet drapes covering the main window, I have managed to make it sound pretty good. My only major remaining problem is that the room still has a lot of flutter echo. I am looking for good economical treatments to solve the problem. Thanks.
Check garage sales and antique shops for a folding room divider or screen. They come in many sizes. Some 3,4 and more folding sections. This can be covered in any favorite material and placed in a strategic area to work great and actually look nice.
Owens corning 703 ridgid board covered with a roma wool.I did 16 24"x48" for about 300.00.Two inches thick.Come to find out four inches would go down to 500hz.
Bosch, are you the one who posted about doing a diagonal room setup? I am, too and for the slap (flutter) echo I purchased two sets of Golden Sound Acoustic Discs. It was either those or buying/making triangular pillows. Having heard the DIY room lenses in action, I decided to go for the Acoustic Discs, as they work similar in principle--diffracting sound waves.

Best in your project, and keep us posted. You can send me a private e-mail if you wish.

i have 1.6 maggies and they are dipolar;i recently bought 2 fake ficus trees and put them behind each speaker.they diffused the sound and killed the slap echo.the sound wasn't deadened and the soundstage remained.
use of absorption material can have an adverse effect on the sound,so use it sparingly.
in your case ,you could use them accross from the speakers on the far wall.the cost is only about 40$ a piece.