I am biased as I am in the ski rental business, but I will copy and paste an answer I give to a lot of people.
This season, lets say you ski for 14 days (two separate weeks), then you can rent in Whistler for around $500 including taxes etc... so if you did that for 3 years, then you would have spent $1500, which is about the same as buying (high performance skis/bindings/boots/ski poles) yes you can buy cheaper for second hand / last years model but thats half my point.
In 3 years time you have broken even, and in the meantime you have to worry about maintenance / transporting your skis. you are also now skiing 3 year old skis.
By renting, you get to ski current season models every year, you get to change skis depending on snow conditions (free to change in whistler, maybe not other resorts), you don't have to worry about waxing/edging/base repair. You don't have the hassle of getting skis on and off planes or cars....
Thats if you hire 14 days each season, it takes even longer to break even if you ski less (obviously less time if you ski more... duh)
If you hire for 14 days straight it costs about $370
If you hire for 21 days straight it costs about $500.
Side note: I DO recommend people buy their own boots - good boots are the most important piece of equipment.