Here is a closed auction - you can look at "seller's other items" to see what is active
http://www.ebay.com/itm/141452048543?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITLooks like the hard to find one range from $12 - $19 or sometimes a few dollars more- but if one seems to be getting high, just check back later since there seems to be a decent supply of all of them. I've noticed a couple of other sellers selling these too, so you might also try searching "mystery mini lyra" or "mini lyra" (or whoever) and in the search options- search only sellers from China (that's what I did)
Definitely cheaper than buying multiple boxes this time- they are cute but I don't need THAT many ponies! I still have an entire box worth from series 1...