you are right, somethings have gone up but used to be staples of selling for 1200cpu like polyplast and electrum now sell for 650-800cpu range
I've been getting about 1,050 for Polyplast and it sells like hot cakes. Electrum is about 700 per unit and is not a fast seller.
On the other hand, things like MK-6 kits were at around 32,000 per and now easily go for about 38,000. I sold ten yesterday in the 40,000+ range.
LOL, things like Biometric Alloy which was in the 100,000+ range go for about 3,000 each. Yesterday I picked up ten (for my own crafting) at 700 each.
Early on I was concerned about being a one trick pony and built a large product base. It has paid off and I stack mats that I know will always be in demand but are selling low at the moment and list / dump the ones that are selling high at any time. Mutagenic Paste always sold at a good price and then tanked. I stacked a couple of thousand of them in my cargo hold. It has taken a bit of time, but the pricing (at least for now) has come back and is higher than it had been. So I dumped a lot of paste this weekend and made a ton of profit.
Except for few specific mats, the GTN market has always exhibited wide variations in pricing for any mat over a length of time. This is because there is not a constant demand or high volume of sales for most items , So my approach is to keep reserves and move with the markets - list what is high and build cargo hold reserves for what is not,