Depends what you're looking to do. ISM bands are limited to 1W transmit power, and the lowest frequency band with more than a few kHz available in the US is the

Depends what you're looking to do. ISM bands are limited to 1W transmit power, and the lowest frequency band with more than a few kHz available in the US is the 902-928 band. High frequency and low power combined tend to mean relatively short range. That being said, I work with 900MHz radio for a living (among other bands), and you can get impressive results in the 1-20 mile range with the right technology and infrastructure. A $10 ham license opens up a significant amount of bandwidth, and power up to 1500W.