This is the cheapest design for reservoir-planter conversions yet!

Lucked out at the dollar store this weekend, here you can see a mesh drawer organizer which fits nicely inside a rectangular planter.  Total cost? $2!

materials: (1) wire mesh drawer organizer, (1) rectangular planter, (4) screws 

Dollar store planters are great because they have this latice design which helps you position your screws perfectly every time!

 Next, drill yourself a drainage hole like so.  Go slowly! Otherwise you'll end up cracking the plastic (like in this pic)

Voila! The finished product! Next up, aeroponic conversions...........