These are real collector items and in a wish list for any serious calculator collector.

Some of the Casio's listed here are not so rare but many people want it, making it hard to get.

SL-800 (any type is rare to find)
FX-1 (the first scientific calculator)
FX-915 (ultra thin scientific calculator, very rare)
Casio Mini (the first true affordable pocket calculator)
FX-502P (the one that Kraftwerk used on the record sleeves of "pocket calculator")
TH-8 (the ULTRA rare smaller brother of the rare TH-10 transparant calculator)
ST-1 (Rare stopwatch calculator but very hard to get in complete packaging without damaged covers)
ST-300 (Statistical calculator, the silver colored one is very rare but there was a small quantity of gold colored produced and they are ultra rare)