Big is right about what you can do for cheap soundproofing, Big is often right here, I do not know why, but seems replicable
Now, with so much holes in your soundproofed room, you might end up throwing your money out of the windows. You might be better off with sound treatments to absorb the sound.
It might also be truth than you cannot soundproof your room the way it is built. If this is the case, do not spend $1,500. Make sure you treat the room so that you have a good sound inside and live with the sound leftover outside
If were you, I would explore more the room in room for $1500. At least you have a real enclosed room with such a design, no window, a door. You can still add the 25 Ga channel as big said and craiglist green glue, not sure about his home made clip but a really good idea on the paper.