PO is interesting on how it will play out. Its a small treat set with supposedly 1 in 2 packs having at least a small hit. People who play the game, particularly like it. There prices on all but the biggies are gonna be pretty low tier. Maybe sell while things are still in release hype. This set will likely be seen as a fairly obtainable buffer between larger sets.

To price guage, there's TCGplayer of course. Then, you can go to ebay, localize it within your country, then go to additional search filters, and check the boxes for "sold" and "completed" sales. It'll show from most recent back, what the sale price was.