Most condenser mics take phantom power, which an AD-20 doesn't provide. The typical partner for the AD-20 is a PS-2 when phantom power is required. If you don't want to add phantom power, you need something which runs on batteries. There are a few decent mics which use batteries, which might be found within your price range, or close to it. Nakamachi CM300, AT-822, Rode NT4, and the C1000S are the first ones which come to mind.