I have to add a cautionary note to using eBay for values. Many of the eBay customers buy to resell, so are not willing to pay much. Some of the glass pieces show up so often on eBay that I think we should give them names. Buyers often buy what is popular at the moment because they plan to resell quickly. This creates an eBay economy that doesn't reflect the world at large. A pw that sells poorly on eBay may bring a good price in a brick-and-mortar shop in the USA. People like pretty things. There are two other things that make bid amounts on eBay difficult to interpret. 1) Many of the things bought on eBay have undescribed damage. Often people such as myself keep bid amounts lower in anticipation of damage, particularly when a seller is vague. 2) Shipping for pws are usually much higher than the actual cost of shipping. It's not unusual to see shipping cost $12-15 for a 3" pw in the USA. They cost $6-8 to ship normally. Bids take into account the padding of the shipping costs.
When I try to find the value of a piece online, I do not include eBay in my searches. There are too many variables on eBay that go into the bid -- e.g. feedback of seller, bad auction timing, poor listing quality, expectation of damage, padded shipping. I prefer to value a piece on the quality of the workmanship and the rarity of the piece.
This is not saying anything bad about eBay. It is a great place to get good bargains. But it is an economy unto itself with inherent characteristics that keep the bids lower than the real world. This is good for retailers because they buy that $20 pw online and sell it in their b&m store for $50 fairly quickly. In my way of thinking, the value would be the b&m value (although as the world goes online more, this is becoming less the case).