Decent, Cheap Altimeter?

I use a CicloSport HAC4, which has a set of altitude functions, including climb grade. But, I think it's about $200, not $90. Vetta makes a model (V100A, I think) for about $100. Of course, every bike or wristwatch altimeter I have seen is based on change in barometric pressure. And none of them (that I am aware of) has a provision for inputting the local sea-level barometric pressure independently as you would have on, say, an aircraft altimeter. So, you use a known altitude at departure for the starting point. The problem is that barometric pressure changes constantly, so the alt reading is wrong almost from the get-go. I've never used mine for anything other than a rough approximation of the climb grade.

specialized makes one that is $100. i found it accurate enough to measure climbing on my rides.