I'll say you an easy way to make a cheap boombox

A preview:

Step 1: Material

You need:
1 box
Minimum 1 speaker(I use 4)
1 switch
1 speaker
1 system of speaker for volume
1 3.5mm male Jack
MP3 Player

Wires
Hot Glue Gun
Soldering iron

Step 2: Make Holes for Speakers

Use soldering iron to make great holes
After, glue the speakers to the box

Step 3: Connecting Everything

Solder every positive together and every negative together

The system of volume from the speaker is different
But there is always 2 wires from the jack, the power source and 2 wires from the speaker (black and red)

Connect the 2 wires from the speaker to one speaker