Not sure how far you can go with AVR and GCBasic. I am sure a lot further than a year ago. There is about zero discussion on the forum about the AVR's, so hard to tell how many people are using them. Built an a-d module for an atmega, tried doing the TWI, and more or less flamed out there.
I could pass along the a-d module, if the current one doesn't work for you.
I see that Microchip is trying to soup up their smaller pin devices, so they are trying to make up at least some of the AVR performance gap.