Hi Richard,
An option could be the Lewitt LCT-840 which is almost within your budget if you can get the academy discount. It's a tube mic with a lot of warmth and air. I own two of these and think they sound amazing. It could be a good supplement to your AKG.
If you don't have a Shure SM7 you might want to look at that as well. It's a great vocal mic that doesn't break the bank.
If you go to the used market you can also get some of the cheaper stuff from Neumann, Brauner or the like. A lot of people is raving about the Warm Audio stuff but I don't have personal experience with those. But you might want to check those out as well.
Best,
Martin.