Embedded newbie seeks help

I've just been hired by a company to do some programming, among other
things...

I've got gobs of C experience, but no experience with embedded systems.

They've been using PLCs and special built controllers, but are running up
against cost, power, and production run issues.

I've been trying to persuade them to use a portable hardware platform,
something that runs linux and can be programmed using C, that way, if the
hardware platform goes away, all we have to do is re-write some I/O
functions and not the whole program.

To that end, I need some basic advice:

A book or web reference for embdedded programming in C and linux.  I've
found a few; it would be nice to have a solid background before I make the
real pitch.

A suitable hardware platform:

Keypad input, 16 DIO, 1 or 2 A/D IO, two serial ports, LCD character
display output.  The cost in small quantities (<10) under $100 or as close
to $100 as possible; must be able to withstand temperature extremes -
below freezing to hot, hot, hot.  Most of what I've found are units that
have lots of stuff we don't need - ethernet, USB, etc, and lack some
things we need, like the keypad input.

Any help at all will be greatly appreciated.

--Yan