I only use the #4 cup for welding small projects or tacking up future projects after the tank pressure drops too low to provide a steady flow of Argon for critical projects. I HATE running out of Argon in the middle of a nice bead!
I don't know what your plans are for welding projects or how much quantity of metal you will need, but I just started buying 90% of my metal for projects from Amazon through their "Prime" membership during the last 2 years, and I really like it. You get FREE 2 day shipping for anything eligible, which is usually limited to 8' lengths of metal, but you could order 10 of them if you wanted to and the shipping is still FREE 2-day or less.
It works good for a hobbyist like me, especially since I no longer get to order 20' material from my previous employer and "piggyback" off the shop's existing order to avoid shipping expenses.
You can get nearly any material you need (tool steel, chromoly, aluminum, hot rolled, cold rolled, stainless, etc) in round tubing, square tubing, rectangular tubing, solid round/square stock, flat stock, angle, hex, etc from Amazon. My biggest gripe is the fact you really have to enter the correct terms into their search box to get the full list of suppliers.
Don't get me wrong, I like to support local business when I can. However, when they charge me incredibly high prices for material to begin with (only comes in 12-20' lengths), then charge me $10/torch cut and $14/saw cut (using a cheapy HF metal chop saw), AND I have to drive all the way over there and back in a truck that gets 8-10 MPG (40 mile trip), it makes me like the internet that much more.
Plus I don't even have to open the gates or leave the property and go out into the big, bad, chaotic world.

I just sit by the door and wait for the big brown truck to drop off my metal. Inside good...outside BADDD!
Andy