I have a Cateye Cyclosimulator which comes with a fan for wind resistance and a magnetic drag disk for hill simulation. It computes wattage and while it may not be as accurate as a PowerTap SL, it was available 10 years ago when the resistance unit on my Sears stationary wore out.
I use it for 'off road' (when I cannot get out)training summer and winter
The magnetic portion for hill climbs as it has % slope on the LCD display.
Typical power 330 watts for 5% grade at 12 mph.
575 watts for 32mph sprint for 30 secs
and for me 225 watts for level3
Yikes the price has gone up 100 bucks sice I bought it 8 years ago !