Acoustic treatment of a small room

Hi everyone, I have been reading this forum for a few months now and i am at the point where i would really like some help. I have a Completely detached room (Not connected to any other building) at the end of my garden which i would like to turn in to a Mixing room for my recording projects. I will be using a computer some near-field speakers, NS10 & MK's and that's about it I could make structural changes to the room, but i can not move any of the existing walls. Construction: The room is built of brick, the inside of the walls are bare brick work the floor is concrete covered with a carpet the inside of the ceiling is plywood the door is bare wood. I do not need any access to either of the windows, so they can and will be coved As you walk in to the room on your right side is a storage area This storage can not be moved, but i do have a half meter space in front of the storage that could be used as space some sort of bass trap. Size: H-2.47m & 2.06m (slanted roof) W-2.14 L-3.95m (with storage area 5.94m) Location: Is about 25 meters from the closest house, but sound is not a major factor as i have been playing music in this room for many years with no complaints, and i am only going to be using this room for mixing. Budget: No more than £2,500 (US $5,000) I am not looking for perfection here, just try and get the best i can from this space. I do have a 3D sketchup file if anyone wants a closer look but the file is 2.8meg too big to upload. Thanks everyone for taking a look.