Stefan Molyneux:
Sounds like a great idea to have a weekly show on an AM radio station, especially if it eventually gets syndicated by other stations.
IMHO if you do something like True News where you detail your take on local/domestic/world events, this would probably appeal to a wide range of listeners. You could then use these segments to segway into exposing more fundamental notions such as anarchism/atheism/UPB/etc. Taking listener calls could also add some drama and comic relief, whilst helping Joe Public hear regular callers' misconceptions being constructively deconstructed.
A format that is quite popular that you could replicate with Peter is the No Agenda Podcast by Adam Curry and John C Dvorak http://noagenda.mevio.com/ . They look at notable and trashy recent news and give their take on them which is usually derisive, conspirational and distrustful of politicians. Note that they are also trying to operate with the donation model since the show has no sponsors. By the way, Curry is currently reading Ayn Rand, so give him a bit of time and he'll be an anarchist someday 
If you're going to do adverts, I'd hope you'd stay away from say Alex Jones' GCN radio show format where there are way to many interludes. It breaks the flow of the show and really doesn't allow for more than 10min segments. Also the ads are repetitive and just plain annoying. A better format is the one adopted by Leo Laporte in his This Week In Tech vod/podcast http://twit.tv/ where he has an advertising segment but which flows in naturally. He chats about the product with the various guests. Currently, he's pushing Audible and asks his guests to pick their audiobook of the week. This is a much more graceful and entertaining way of doing adverts.
Getting $1.5K/month worth of sponsors might be tricky initially,pot so you'll need to identify sponsors inside the AM ground-wave coverage who might be interested in the the targeted listener market.
My 2 cents.
Ruppert9