Is there a cheaper alternative...
I'm not sure. I use the ones offered by Cane Creek and they are still holding up well for me after some years including pretty heavy sun exposure.
Hmm. I wonder if some external force is at work here...perhaps ozone from a nearly refrigerator, freezer, or washing-machine motor? That can cause rubber to crumble in amazingly short order.
How are your tires holding up? Id they are also beginning to age prematurely, that would be triangulation and perhaps confirmation for exposure to something deleterious to rubber.
I ask because when I bought my used tandem some years ago I found the previous owner had stored it in a laundry room. It seems the concentrated ozone from the electric motor largely dissolved the previously good tires in just a few weeks' time. It also hardened and embrittled the vinyl covers on the saddles originally fitted to the bike. The cracked also. The rubber handgrips (I changed to drop 'bars) turned all soft and gooey in the same period, so pretty much all rubbery stuff was adversely affected.
All the best,
Dan.