I've been using an HP 11C for over twenty years. I bought it sometime after I started teaching here (1985) and before HP discontinued the 11C (1989). I now use TI's at work so as to be compatible with my students, but I still use the 11C almost daily at home. I just looked on eBay and found a nearly-completed auction for an 11C with a high bid of just over $100. That's about what I paid last week for an HP 50g (the current top of the line) on clearance at Best Buy! Also, there are a couple of 15C's (similar to the 11C but can also do matrices and complex numbers) about to go for over $200.