You can't block light in one direction. If it comes in, it also goes out.
My foam shades cost about $2 each, as did the blackout curtains. $20 each is a lot of you have a lot of windows ;).
I roll or fold my shades and put them under the bed. The foam ones, all together, make one cylinder about the size of a roll of paper towels. The fabric ones fold to about the size of a pillowcase.
(BTW, in my van, I find that weight is a bigger problem than space. If I fill up all the storage space, then I am over the weight limit for the axles. Don't forget to weight your van before you get on the road!)