What about concrete pillars used for planters, could then be used in garden when finished.
Alternatively take some 18mm mdf cut out (this is for one stand ie each) rectangle 1 inch bigger all round than your speakers, then another 2 rectangles progresively 1 inch smaller all way round stack these together evenly so that they resmble stairs on each side glue together and leave to dry obtain some Cardboard cores from your local carpet store and cut to roughly height of speaker stand cut out disc of mdf to fit inside this core snugly and glue and screw this circle to centre of 3 pieces of mdf you made earlier and make sure you put it on the smallest one, do same for base you could possibly make squares bigger and screw in spikes to each of for corners so biggest square is on bottom and circle is again on smallest glue cut carpet core to circle and fix with screws if you like then plaice other sqares on top with largest square upermost , before you place3 top on fill column with sand and paint a fetching colour, plonk speakers on top and wait for shop bought to arrive, shouldn't cost any more than a tenner plus spikes (which are optional), hope this is not to confusing and you get the drift, they could be used as planters or lamp stands later, you could also cover them in modrock and make some wacky scultural look but ,........ I think I've gone and taken it too far.