I have not been to Mountain High. I’ve been to Big Bear a few times. Skiing/snowboarding is fun, but it is very tiring if you’re not in a good physical condition. After an hour you’ll pretty much want to tear off the boots and sit in the snow.
You can buy a day pass and rent the equipment on the spot. Day pass for Big Bear is ~$50. Equipment is ~$25. Bring pants/jeans and a jacket. Local stores sell cold weather clothes (insulated pants and such), but prices are outrageous. It’s not all that cold (our “ski resorts” get to 50 F during the day). Your main concern is to keep snow out of your boots and sleeves.
It is easy to put chains on tires, it takes 10 minutes with no prior experience. Chains/cables are purchased at Wal-Mart for $20. Be sure to check the owner’s manual of your vehicle to see if it’s compatible with chains or cables. Once they are on, you drive as usual, but it’s very noisy and you’re not supposed to go above 25 mph.