Auralex subdude isolation platforms under Ohm Walsh speakers about $100.
Isoacoustics stands under various small monitors also about $100.
The simple Monster power strip my preamp and source devices are plugged into cleaned up the sound for about $70.
Auralex 24x24 inch acoustic panels at prime side wall reflection points about $35 each.
I've bought gear on audiogon but not tweaks in that the cost for basic things that work like these are extortionist mostly here.