Probably the place to get started with backcountry gear might be to go to
Outdoor Gear, Clothing & Footwear at Eastern Mountain Sports (EMS), and search under skiing gear for backcountry gear.
Skis: $200 to $400
Bindings: $50 to $80
Boots: $125 to $150
Poles: $40 to $50.
Watch for sales. Ski equipment usually goes on sale starting around Feb 1.
Where to find skins: where every backcountry ski gear is found, usually at outfitters rather than alpine ski shops that cater to the downhill crowd. I don't know where you live, but there is probably a local outfitter, or a chain store like EMS or REI