Hi there.
I am also considering a trainer. From reading the reviews I was considering the Great Planes PT-60. The only thing that Sig has in this size is the Sig Rascal... and I'm sure that's probably not what I'm looking for.

This trainer will have last 2 training pilots, one after another. The Pt-60 had a good review with some options as you build it. I'll be using it as a 4 channel and then back to a 3 channel for my wife (she hasn't had much interest in aircraft until she meet me about 3 years ago).
As for a powerplant, I was thinking along the lines of either a Evolution NT .61 or a Thunder Tiger Pro .61
As for the radio... well let just try and find an instructor in my area first!!! That AMA site wasn't up-to-date on it's information, which I don't blame them (AMA). So right now I'm just waiting for someone who I contacted on this site under the 'find instructor' area of this site to get back in contact with me.
I been considering the Hitech Laser 6 - I have heard many pros and cons on non-computer radio's, but what is getting me is my budget and how much I can spend.
Good luck,
Mr B.