New to tube rolling, where to purchase tubes?

I have always been more of an SS guy but now have a Monarchy DAC24 with a tube stage. (run through Ayre AX7e and GMA speakers). I am not crazy about the sound of the tube stage now (too euphonic) but imagine with the right tubes, I might find a good match for the Ayre and get a "rounder" sound. At least, reading the tube roller forums seems to indicate that might be true.

The tube stage has a pair of Phillips 6dj8s. I would like to try some different tubes to see what effect it has but would prefer not to spend a ton at first and have no idea where to buy tubes without getting ripped off.

Questions:
1. who are reputable dealers for tubes?
2. would I hear a difference if I spent $100 on a pair of older matsushitas or must I spend a bunch on vintage amperex to get a significant change in tone?

thanks.