I use Sorbothane inserts because I prefer cushioning under my feet rather than support under my feet. My support inserts are in my off-road running shoes. I bought them from Ebay, very cheap, £10 at the time.
I'm not suggesting I'm right but I can't see how expensive inserts can be that much different from cheap ones? In one of my pairs of boots for example, I have Aldi ones, £2.99 and they are great.
If however your feet have special needs then my entry may not be useful information.