Having a similar debate with myself now. We go through pillows quite frequently as the dog(s) are allowed on the sofa. Sometimes they just get grimy and can be laundered but then there are the times when you get the tears or big scratches.
So I've been debating about getting the forms and just making covers as needed vs getting new pillows all the time. But like you, look at the cost of the forms vs what I can get cheapie ones from Walmart; Target; Kohl's and then just end up buying new ones for expediency.