Ah yes, I don't really think that the price is something to worry about. It would be a rare and got when using three different cards (fossil+rewind=bones+spell=creature)
Anyways, I'm gonna finish the series sometime and all the cards will be explained there.
Not to force you or anything, but I personally believe it's a much
smarter idea to fix any errors you have on a card idea before sprouting new ones. This way, you don't have to worry about making dozens of edits to all of your old cards (to the table, card art, description, costs, name, spelling/grammar issues, etc.), and you'll also have an increased chance to allow your cards to 'flow' into one another by providing links to the finished cards within your Series.
Also, I don't think the link you provided credits the artist properly. You should/need to give a different link to your picture instead.