For your budget I can recommend two very nice sounding mics. The Roswell Mini K47 does a good job on double bass. I do not own one but I have 2 friends that do and they like these mics very much. I've heard them and there's a lot of bang for the buck with these cool, little mics but as with all mics, YMMV depending upon quality of your recording chain and room acoustics. The other is a mic I love. It's a passive ribbon microphone, the Samar Audio AL95 and it has an extended low end response that must have been made for recording double bass. Its' $400 and is, literally, a world class microphone at a bargain basement price. You will need a high gain preamp, or add a Cloudlifter ($150) to the signal chain, as this is a ribbon and all passive ribbons need the extra gain. If you have the preamp power, IMHO the Samar cannot be beat. I've used a Samar VL37 on everything from my bass, to violins to saxophones and it excels on all of them. There's a lot of magazine and online reviews so you don't have to just take my word. I think Samar's ribbons may just be the best kept secret in the recording world right now.