A couple more to add to the list: Kit Young Cards
https://www.kityoung.com/ has been around for a long time. It seems like they are still grading like it's the 1990s when things were a little less strict. This makes it hard to find bargains, but if you do find one, you can buy direct from their website and avoid tax.
Another dealer is
https://www.amerlegends.com/ which has a brick and mortar in Scarsdale, NY. Their cards are listed on ebay, but you can email
mark@amerlegends.com to get a 10% discount off the ebay price, which tend to be pretty reasonable to begin with.
Yet another is
https://www.starxcards.com/ which sells on ebay, but if you buy direct through their website, you avoid tax and shipping costs.
Also,
https://www.bleacherbumcards.com/ lists their cards on ebay and has mostly modern with a few vintage, but you can get a 10% discount or so through inquiring on their website and avoid fees.