A few years back, I bought used Kreitler rollers for about $130. I then bought a $20 magnet on Amazon. Stuck it on the frame (Fe based) right next to but not touching the Al roller drum. Cheap DIY resistance that is relatively quite and can be folded up to take to races for warmup. I can perform interval workouts hitting easily over 500W and not spinning out. You could put two magnets on there for even more resistance but for me that is basically sprinting and that workout happens outside.