There are online stores on Easy.com that sell downloadable digital prints.  I love this one from Cre8T which is only $7.18.  You can print an A3 size poster of it at K-Mart for only $14 and buy a frame for $4.  
You could print out a smaller copy for less.  It would make a great gift or decoration for your room.

If your bedroom needs a makeover, consider a chalkboard wall (check with your parents first).  A can of chalkboard paint will set you back about $15 at Bunnings.  This one is from is from www.boredart.com. 

Here is an easy holiday craft project - a butterfly collage.  All you need is a photo frame, some scrapbooking paper, a butterfly punch and some glue.  You can find instructions at www.theidearoom.net.

Check out this and other great decorating ideas at decoratingyoursmallspace.com. You can find them on Pinterest too.