Eco Complete is the best inexpensive "planted" substrate IMO
. Not sure elsewhere, but on Amazon it's 20$ for 20 lbs. Sand is inert, I wouldn't recommend it for a planted tank unless you're using it as an accent to your scape (i.e. riverbed, shore, etc.) or as a cap... some people who want to go even cheaper use organic miracle grow capped with sand. But Eco complete is worth the extra cost as it's easy to work with, not messy, plants root well in it, has trace micro nutrients, an attractive substrate, and has a high CEC (hint: research "CEC and Eco Complete").