Rubber footers are not the best for coupling speakers to anything.
Here is a budget alternative that I have found works very well on hard surfaces - a very thick/heavy chopping block or cutting board (Maple, bamboo or similar material), slightly larger in area than your speaker's base. Separate from and attach your speaker to the wooden "platform" with four small dots of blutack or similar adhesive. Remove the stock rubber feet so vibration drains away from the speaker through bluetack into the wooden platform. Try with wood platform either directly on the floor or with blutack attaching it to floor too once your speakers are properly positioned in the room. Experiment to determine which configuration sounds best to you.
This REALLY cleaned up the bass on my set up, and improved treble definition at the same time - or perhaps I could just hear things better once muddy bass fixed.
This solution can be done for significantly less than $100, depending on your access to good quality wood slabs/cutting boards. Try a commercial kitchen supply store or the Internet.
The next step up in cost and complexity would be to use 3 or 4 brass cones or other metal "points" between speaker and wooden platform in place of the blutack, and between the platform and floor, as sounds best to your ear. This solution can actually reduce stability, but will be more similar to steel outrigger and points you describe in terms of function and performance.
Brass cones can be quite pricey, but work well in most applications.
Check here for visual description of what I am talking about:
One final suggestion would be to get some Totem Acoustic "Claws" - see here: