The one I have now is pleated... I think the manufacturer does not recommend backwashing, but I'm backwashing it after use with fresh water for 20 mins, then a final backwash with star san. I'm really not sure when I'll retire it, but I'm guessing 5-10 kegs ??? I'll probably go by smell and sight - if it smells clean and looks clean, I'll still use it.
The $90 ones, especially if you go for the stainless reinforcements, can be repeatedly cleaned and re-used, according to literature.
But keep in mind that 'pricey' is a relative term; if you're comparing a $34 or $90 cartridge that actually works to a $5 or $10 cartridge that doesn't actually work, then you're comparing apples to oranges.