I have to agree with "brainfart" to some extent...
Changing to a cheaper resin with similar properties is fine, if you are not depending on the approvals of the resins for aircraft or the like. On the issue of bulk buying, you may not save a lot of money buing a cheaper resin for the parts that needs no approval.
Its all in the balance of costs and amounts used..
Most of my composites work is experimental, I only produce very few "copies" of the parts I make, and most are "one off specials" made for myself and friends.
So in my case, I buy almost nothing in bulk, certainly not resins and hardeners, unless I really need it for larger projects. Especially hardeners, which certainly have a limited shelflife
So far I have tried several resin systems, and really found very little difference between them. This goes for structural strenght too, some of my parts have been built and used for structural tests, and in some cases we could not measure significant differences between identical parts made with different resin systems, case in point being a beam type part made for testing molded in Titanium fasteners.
it was made with both West systems 105, and EC EL2, giving nearly identical measurements, with maybe a slightly stronger result for the EL2