I rented for 3 years at the cost of $5 per month, that's about $180 down the drain.

I finally bought one for $50 after rebates, and it's been 2 years, so I'm ahead $70 right now. Even if it dies I can go buy another one and still be ahead of the game. I predict the modem will last another 2 years easily, so I'll be ahead altogether $190 when it's all said and done - if the cable modem dies in 2 years or I upgrade to a newer unit, assuming the cable company doesn't increase the rental on the cablem modem (although it's highly likely they will - they may have, even, but I don't know since I no longer pay rent).

Buying always trumps leasing, if you need the service for a long time.