Need to know what I need to do to install electric baseboard heat in my upstairs bedrooms. I want to get 3 1500 watt /240v heaters. Can I put them on one 30amp breaker with 10-2 wire?

I have a 100 amp service panel that's maxed, can I add a sub panel without upgrading to 200amp? Currently I have one 50amp range breaker, two 30amp breakers (dryer & air) and then the rest are 20amp breakers for lights, plugs, etc.

I plan on using these heaters only at night, approximately 8-10hrs.

Other question: If I need to upgrade then maybe a ballpark figure of what you think it would cost.

Any wisdom would be greatly appreciated.

Thanks

Mike