I wouldn't even worry about the front/right and rear/right corners, perhaps. Definitely not superchunk by any means, IMO. The bass waves can still wrap/diffract past that corner I imagine, and I just don't know if it's worth trapping for low bass there. We need an expert to chime in so that I don't misinform you any further.
My guess is that an expert would tell you that thicker panels, and more of them, behind the listener. Thick enough to absorb bass, as the bass will be collecting there. While more bass doesn't seem like a bad thing, the problem is that it may mask your other frequencies.
In all honesty, depending on what your speakers are, I'd take all of this budget towards new speakers. You seem to have a penchant for DIY, and if you were willing to build speakers, you could potentially find tremendous value.
Check out the ER18 build for instance in the DIY subforum. The silk dome version comes out to $551 for the pair as of several months ago, including even the spikes. But it doesn't include the wood and glue, which won't be too much. The speaker that it most closely resembles costs $4,200, by the same speaker designer (although it uses superior drivers, if still made by the same SEAS company). I throw out this idea, just in case, depending on your current speakers. I suppose the problem is what you can find in Estonia (I've driven through your country once, heh), however I am sure there must be some good European DIY resources. If this sounds interesting, I cannot think of a better person to ask than TLS Guy as far as European DIY resources are concerned.
