What are you using 303, 304, and 316 for?
For homemade fishing lures, like this fella:
https://alantani.com/index.php?topic=29069.0
This place appears to have the best prices in my area:
https://www.coremarkmetals.com/
..especially if I buy from the surplus section, as it comes out slightly cheaper by the pound and avoids the cutting fee. They typically have 3 or 4 foot round bars for my purpose. After procrastinating (and making other types of lures) I recently started working with 1/2" 303 round bar, and it's a lot easier than I thought (was afraid) it would be. With a cheap hacksaw my forearms feel like Popeye's fairly quickly...
The only thing is, with the surplus section you don't know if you are getting 303, 304, or 316. Most likely 304, I would guess.
by the way, in 2016 I believe I paid 5 bucks for a 303 24" 1/2" round bar, and now that same place (different supplier from the one mentioned above) wanted 15+ bucks..another one, since it was "special order" wanted 45 bucks. What the hell...
Ideally, I would like to go the cheap bastard route, but anything in the free craigslist section is either massive refrigerators, microwaves, etc, with sheet or plate stainless...