Landscape Plateblocks

In the last week or 2, I have seen a ton of landscape plate blocks listed on E-bay. The majority of them are listed as buy-it-now, with prices less than 50% of the Bale catalog value. So, it makes me wonder, how accurate is Bale in valuing these? I have never seen these offered by any dealer at a stamp show. Unlike US stamps, Israel plate blocks seem to be collected rarely. Of course, there is some good news. I am down to needing 14 out of the 170 different printing dates. The bad news is that 11 of the 14 are expensive, with 8 of them being greater than $100, and at least 2 of them greater than $1000. I haven't seen the 3 relatively inexpensive ones (< $20 each) listed on E-bay yet, while 8 of the other 11 are currently listed on E-bay. Some of them are being offered as full sheets, which are obviously more expensive. I have picked up some of the full sheets to fill in some missing printing dates, but only when the cost was relatively low (usually under $5).