You can get a used nikon d5300 plus conversion from Lifepixel for US$554 plus post.
You can also get your 600D modified at Camera Clinic in Melbourne, but the 600D is much more noisy than the nikon.
I've kept our Canon 600D as a daytime camera and moved to a nikon d5600(similar to d5300) to get away from the noise.
I modified the d5600 myself using the Lifepixel guide; they also have a guide for the 600D if your good with a screwdriver and tiny screws