We are lucky to have so many suppliers in our hobby that are good.
I always do a side by side price comparison on suppliers that have parts, if multiple suppliers have them. Helps me keep all my games going, helps me spread the love around to the sellers who have helped me keep my beloved pins going.
Nothing is worse than having to place an order from 2 suppliers when 1 of the 2 suppliers has everything you need but 1 piece!
I keep a running list of things I need from any given supplier, to keep my inventory current. Some things, I have before I need them. Cleaners, coil sleeves, rubber, flipper bats, leg bolts and levelers, connector housings, pins, fuses, rebuild kits etc. Stuff I'd consider generic 'supplies', or stuff that I might need to fix a board or game that someone brought by for a repair.
Some places, like PBR, have discounts at the $100 level that make buying from PBR a plus.
I don't reorder the supplies until they get to a restocking level, and then I shop around for the best price.
Or, if I need something from PBR, for example, that only comes from PBR, I try to make sure I include enough parts off my wanted list to pad it out to get the discount at $100. I know people who have told Steve in the past that if the order was close to $100, add #44 bulbs til they hit $100, just for example.
If I need just 1 part from Marco immediately, I add the stuff that's on my 'to be ordered from Marco' list, so I can divide the shipping across all the parts - although, Marco's shipping seems to be a lot more competitive than it used to be. It used to be, Marco's shipping seemed like it was obscene when compared to other suppliers.
And, some suppliers, like MAD, have stuff I want, but have heard enough horror stories lately that I'll pay more to get the parts elsewhere, and in some cases, do without, if MAD is the only choice. Hope MAD cleans up his act, as I like doing business with him!