think outside the box

i am gonna build my own sub box, should i use MDF or block board plywood, and about how much does each type cost

MDF is the best. Most places a 4X8foot 3/4in thick piece of plywood is about 20 bucks. Home depot, Lowes, etc...

i used 1/2" plywood with silicone calking and some steel to make sure its a good fit, a lot of work to save a few bucks, dont be cheep like me and spend the few extra bucks for mdf

Never use plywood.You can use particle board, a little bit cheaper than mdf.