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) Price between 30 US$ and 200US$ (depending the full packaging and condition)
FX-1 (the first scientific calculator) Price starting from 100 US$ and Up
FX-915 (ultra thin scientific calculator, very rare) Price starting 60US$ and Up (in 2007 one was sold on ebay for 320US$)
Casio Mini (the first true affordable pocket calculator) Price starting 30US$ and up
FX-502P (the one that Kraftwerk used on the record sleeves of "pocket calculator") Price usually goes around 80-120US$
TH-8 (the ULTRA rare smaller brother of the rare TH-10 transparant calculator) Very rare , Price starting 200 US$
ST-1 (Rare stopwatch calculator but very hard to get in complete packaging without damaged covers) Price starting 10 US$ and up
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) Price starting 25US$ for the silver and over 100 US$ for the gold version
FX-98 Very sought after by collectors and pretty rare to find (in 2011 March one was sold on Ebay for 485US$)
FX-98(B) Ultra rare version of the FX-98 ( priceless...)
FX-48 Another credit card sized scientific calculator (very rare, prices goes around 50 US$)