I've read before that as the spark plugs wear down and the gap gets bigger; it puts more load on the coils and that's what kills them.
How old are your plugs? What's the gap set too?
If you get new plugs; set the gap at the smallest spec so as they wear; they last longer then setting the gap closer to being out of spec.
Check on here for various brands and check prices on the coils that are out there:
https://www.rockauto.com/Also check Amazon and ebay for coil prices.
I'd personally put new plugs in and a fresh set of coils and keep the old coils as spares.