Dollar General Newborns
These were sold for about a year or two at Dollar General stores in the US for $1. They came in a full rainbow of colors. The plastic/vinyl is a lot thinner than real MLP newborns. These are often used in making customs. They are moderately common.
I have a purple one (seen in the photos) that has no mane as a result of a factory defect. I've seen the same defect on a few of these in eBay lots. Apparently the manufacturers don't care about such big flaws.
I am told that they are now being sold at Rite-Aid drug stores for $2.99.