There is one advantage to buying a full setup & that is you have stuff to sell to offset the cost of buying what you want when you've figured out what you want!!
this can all work quite well if your buying it second hand.. I've lost a bit of money on the four different scopes I've had on this gun but it's not much probably about £50 after selling the scope the gun came with.. which isn't bad as 2 of them were new., And I've had use from them. I think it's great chopping & changing on the second hand market until you find "the one".
Rhys