the cheapest thing to do is build yourself a
HOB skimmer. you will not need an overflow. the skimmers pump will hang in the tank and supply water to the skimmer. the discharge will then drain back into the tank.
you can save even more money by not using a DSB.

you can save even more money by using concrete, oyster shells, and sand to build your own LR.
theoretically i can suggest things that will get you a full blow reef tank for less than $500. you may not like the look, but i can suggest alternatives.
G~