I too have struggled with getting spinach to sprout but I came across a post on pinterest that has worked for me. Put your
seeds in a zip lock bag with about two inches of water and throw it in the refrigerator. Leave in there for 24 hours then plant. I used the rapid rooters, wrapped the whole thing in cling wrap and put it on my a/c vent. Four days later I walked by it and had about an inch long sprouts.
You can get free bottles from a water company just by asking. They will give away bottles that have leaks and usually mark the leak with a sharpie. Just make sure the leak is in the top 1/3 of the bottle and it will work. The bottles without a handle work the best. I painted the one for fair black then white but I think I am going to mod podge the second one with some craft paper.