Talk:Free Charge Controller
The programmer is out of stock! Haven't had a look at the resources you require yet, but is there any chance you could do this project with an MSP430? At $4.30 the LaunchPad is a complete development kit for harnessing the ultra-low power and 16-bit performance of MSP430 Value Line MCUs Can't beat that price, and it includes the programmer. I've done several successful projects with MSP430s and before I ran into your project planned on doing this (some day) with the MSP430 If it would fit into a -2012 or -2013 you are talking about a $1 (+/-) for the CPU! If you need more resources it's always easy to move up to next level. Available in PDIP and SMT, I've used both.
Plus they have their own WIKI so programming support is available for the newbies. http://processors.wiki.ti.com/index.php/MSP430
How wedded are you to AVR? Isn't it mostly C? I think you will like the simplicity of using the ADCs and PWMs in the MSP