Lift tickets average somewhere around $40 to $50 per day
Where are you going skiing? Most resorts I've been to charge $70-100+/day (in Colorado).
Expenses to consider include:
Lift ticket - the resort should have the prices for individual and multi-day passes on their site. If the price per day is about the same, you might want to buy your ticket one day at a time. That way, if you're totally worn out after the first day you can take the second day off to rest without feeling like you're wasting the money. Many ski slopes will also have a sledding hill, or you could hang out in the lodge with a good book, or wander around town, etc.
Equipment rental - again, prices should be listed on the website. It might pay off to check out rentals at near by shops. The skis/snowboard, boots and poles usually come as a package. If you can, I suggest renting a helmet and goggles as well.
Cold weather gear - I forget where exactly you are but seem to remember it's some place warm, so depending on the time of year you might need to buy heavier gloves, coat, etc. Don't worry about buying special ski clothes. Snow pants are nice but you can ski in jeans, although I do recommend wearing tights or exercise pants under them. Some resorts will also rent out ski pants, coats, etc. I've skied in everything from single digits to 60F, so this is one to keep an eye out for as the time approaches.
Food - Yes, resort food is typically over priced, however most have a dining area open for sack lunches if you want to bring your own. Typically you'll only eat lunch on the slope, what you do for the other meals depends on where you're staying.
Locker rental - I'd avoid this one if you can. I'll ski with my shoes around my neck before paying for a locker! Yes, I've done this. Instead, plan to take a small backpack to carry shoes, water, snacks, etc. Lockers can run anywhere from $2/access to $10+/day.
Transportation - How are you getting to your lodging from the airport? How are you getting from the lodging to the slope? Many resorts have lodging that's right at the slope, but if you're staying in town you might need bus fare or a rental car.
Those are all the expenses I can think of off hand. With the ski season just getting started there are a lot of deals being offered so I'd suggest looking for coupons online.