I have had at least my share, or more of scope failures! And I am not really hard on scopes! I have had 2 Tasco's fail. (one failed, they replaced it and the replacement failed) I was THROUGH with 100.00 range scopes!
I got a Simmons Aetec, it lasted 5 years and this year it failed!
I thought exactly like you are thinking, until the Aetec failed me!
I thought that the Aetec was a great scope, and I am a "frugal" shooter too! SURELY, scopes costing 3, 4, or 5 times more COULD NOT be 3, 4, or 5 times BETTER than mine!
I WAS WWWW.......WRONG!

There are two things that I'll grant you:
1. ANYTHING mecanical, and man-made CAN fail!
2. Most scopes have the clarity, to at least make 100 yard shots in LEGAL light!
That is where comparison between cheap, err frugal scopes, and better scopes end!
Better glass does give you much better clarity, especially in shadowy areas, and the extra clarity DOES help (especially with the eyes getting older!) and DOES cost extra!
Craftsmanship, materials, and QUALITY CONTROL, COSTS MONEY!
That is to me, the big difference in scope costs!
It is what we really CAN'T SEE, that counts!
With better quality scopes you are LESS likely to have a failure!
Having had 3 failures, I hope I don't get a "lemon!"

Finally, being a "frugal" person, is a 1000.00 scope better than a 400.00 scope? I seriously doubt that! But... I've been wrong before!
I DO KNOW that even with "cheaper labor" a 100.00 scope IS NOT the quality (materials alone) of a 400.00 scope!