Assuming the council would play ball, and AFC would be willing to increase their budget for land purchase, the current AECC site would be ideal. Shouldn't be much issue with the roads, especially when traffic can head north towards the AWPR. Plenty of public transport already in place (including a Park and Ride service on site). There's a couple of hotels right next door, we could even take over the existing office building and viewing tower if the council wanted their upkeep off their hands, plenty of room in there for hospitality facilities, museum, corporate offices, etc.
There's not many residents nearby to complain, and the site is already used for large-scale events so it would be hard to take any noise complaints seriously. If the stadium could be build within the footprint of the existing exhibition halls, there would be masses of parking spaces surrounding the stadium, one would assume we could use them if they're already there. And renting out the car park for Elton John concerts or Monster Truck shows could generate some revenue without destroying the pitch.
There may even be a possibility for a formal arrangement with the Gordon Barracks to build training facilities considering we've been using their land for training for years. I see 2 full size pitches there on Google Earth. You could convert the exhibition hall that's next to the hotel into indoor training facilities. Not as fancy as the facilities at Kingsford, but should be much lower cost considering the bulk of the facilities are already in place.