Keep in mind that dsb and rdsb are both recommended to have sugar fine sand and a high flow rate. The amount of sand you are wanting is enough to filter a tank roughly around the 600 gallon range.
If I remember correctly, 40 lbs of sugar fine argonite is enough to fill a 5 gallon bucket 3/5 of the way. You'd be looking at between 500-700 lbs of sand.
It might be a good idea to look into other alternatives for places that don't require sand (like a turf scrubber or algae). Most of the benefits of a dsb are more effectively replecated in other ways.
We decided to use mostly organic filtering for our tank and plumbed in a rdsb(so please don't think we are against them) But even its strongest proponents say its not the end all, be all. Save time space and money and look into other alternatives.
IMVHO.
Ps, I'm also aware that I don't know exactly what it is you are going for and have prepaired my foot for mouth insertion if need be.