I have a box of several hundred old cassettes…. some of the specialty ones are still quite useable, (oldies, big band) but you are right the premixes of the 80s and 90s are dated.
I favor power music and dynamix, but I have used Yes! and I think they have some programs where clubs can get free music to incentivize their instructors. you might look at their web site.
Of course it can get expensive to change up a lot, and Harris is right, if you do not mind mixing for yourself, and your club is paying the licensing and other fees Harris is right something like Pandora can work.
It seems to me that someone suggested a podcast by someone called dj kj, who had a pod cast and sold music, but also gave some workout music away. I have never used them, and not sure if they still exist, but you could look it up.
Lastly, I know it isn’t what you asked, but I would like to put in a plug for buying from a music service.
The two biggest advantages of premixes are that the music flows and the tempos are even (and the speed you want), and the licensing fees are taken care of. Also downloading music for your own use is quite different from using it for a for profit class…. for which by law there are usage fees.
I personally like to buy music. I know some musicians and they have the same expenses I do and just as I hope people will like my classes enough to pay (and need that to happen if I am going to be able to afford to continue teaching) I want to support the people who are providing the music I use in class.
I also LOVE how now one can buy single songs and mix a play list without getting pieces that one doesn’t like or finds inappropriate.