This is a bit of a tricky one but might as well throw it out there and see what people think.

http://i.imgur.com/Rii8tFv.png

So I've bought this set with 92 Escapists in it (91 counting the one that came with.) I paid 70 keys and 5 ToDs. To get the price of the kit, the cost of the Escapists already in it need to be removed, so that's 91 x 1.55 = 141.05 refined. At the current cost of 15.77 ref per key, that's 8.94 keys which we might as well round to 9.

Since ToDs are just about half a key, we'll say those add up to 2.5. So the sale was for 72.5 keys, 9 keys removed for the current contents, we get 63.5 keys left. Woop.

Obviously this is a little weird territory when it comes to pricing, but it should be close enough to work out just fine.

Edit: Forgot to mention, the last sale of this set was in February, thus too old to be used, and this is the only known set, so there are no other sales.