Midwest is cheaper than Online Metals. By a lot. They are also very very very very very (maybe one more very) very slow to ship. I've canceled a few orders due to waiting weeks and weeks and weeks.
Xometry is also cheaper than Online metals on most things, but they have a fairly limited selection. They are competitive with Midwest on single piece units or atleast close, but they give no quantity discounts. Midwest smokes them on quantity. Xometry smokes Midwest on service time. They almost always ship by the next business day, and sometimes the same day.
For aluminum and stainless in any quantity at all (full bars/sheets only) Coast is the best price, and they send a truck to my town twice a month. $50 drop charge and $16 order PO processing charge. They waive the drop charges for modest size orders. Their price is good enough that I can often break even over buying from a local yard on one or two pieces. I try to stock up a little whenever I have money and I save a lot. They give a small discount at 500 and 1000 lbs. Usually I am ordering a couple hundred pounds. Like I said even for one or two pieces I tend to save over my local metal yards, and its a lot cheaper than the truck freight from XoMidCarrOnline.
For small pieces I always check McMaster. Sometimes they surprise me. (Usually they don't).
Another to check sometimes is Stock Car Steel. I used to buy precut aluminum blanks from them, but their price is only mediocre and shipping fromt eh East Coast was always an issue. Not as bad as Midwest, but it takes time. (Nobody was as bad as Midwest for ship time.)
Stoner Materials is worth a look as is the 6061dude. Heck Ebay can be a good resource for small pieces although more Ebay sellers are charging close to retail metal yard price for the drops now. That's ok if they have the size you want, but kind of a pain if you still have to preprocess it.