If you keep your media clean, it lasts for a very long time.
I'm still trying to finish off some corn cob that was purchased in 2007 (10 lbs, and I
just got into the second half of it). With another 10 lbs sitting on the shelves... I won't have to buy corn cob media again, until 2020.
I'm still using rouged walnut I bought in 2008. The 3 lbs in the tumbler still has at least two years' worth of use in it, and there's another 6 lbs in the jug. Like the corn cob media, that should last me beyond 2020.
I only tumbled about 7k dirty cases, last year. By all accounts, that's pretty low (and doesn't include loaded rounds going through to remove case lube). By keeping the media clean, it just keeps chugging along...
At this rate, I'll be HAPPY to spend $1/lb on "premium" corn cob media and $2/lb for rouged walnut, when the time comes.
Besides... Most of the media marketed to reloaders doesn't have all the dust and chaff in it, that you get with the alternatives.