We got some fairly plain, inoffensive, thermal backed curtains for the kids bedrooms in the Warehouse for less than $200 in their sale - they block out most of the light. By inoffensive I mean plain in colour and not that kind of pattern you need to wear sunglasses to look at
If you are having trouble sleeping though maybe worth looking bed time routines etc to see if that impacts on getting to sleep.... I had real trouble sleeping about a year ago and went to see a herbalist who advised me on my diet and I also take a magnesium supplement which has made a big difference.
Best of luck
Karen