For a 48"x18"x20" tank you'd need about 85lbs of sand to give a 2" layer, pool filter sand is probably the cheapest way to go, or you could mix pool filter sand and caribsea substrate if you're going to have plants.
+1 to pool filter sand, really cheap, looks nice - can't really beat it
just make sure to rinse it REEEEEEEEALLY well with a bucket or something before adding it to your tank, or else you're gonna be trying to look through orange water to find your fish lol
I'll say u only need about 1 inch of sand on the bottom if you are having fish-only tank and the fishes are not burrowers. Else pocket of anaerobic bacteria could form and produce H2S.
Cleaning the sand would require practise but it would be easy once u get used to it. Just siphon near the sand to remove the gunk ontop of it.