Here's my strategy:
1. KNOW WHAT YOUR TIME IS WORTH. I'm self employed and if I can't save at least $1/minute (should be $2, but that's assuming I can ALWAYS earn my full rate, which I sometimes can't and $1 is just a simpler number). Use this to stop looking for a better deal on a $50 order. If you try to get it down to $45 and spend 10 minutes ($10) trying to do that, you've just wasted time (and therefore money!).
2. Online ordering is the #1 way to save time (and likely money). I order a lot of fixture parts on McMaster. Easy to filter & find, always good quality, seconds to place the order, fast-enough shipping. I have just found that "dinking around" on MSC or another site is just too much time and knowing the brand just isn't that important for my stuff. That trip to an industrial supply store will be time consuming. However, if you can establish an easy way to order with a local supplier, I do like supporting local brick & mortar.
3. For materials, the same thing usually applies. If I am ordering fixture parts, and my tool & die machinist needs so material (usually not a lot), I just place the order and have it all shipped to him (easy to do on McM, he's another ship to address that I can change with a click). He'll give me the fixture parts. If it's more, or I don't have parts to order, I'll go to Metals Supermarket but I have to do a phone call (their website sucks) but I have established a good relationship and sometimes they'll ship in their truck. So, MS is usually cheaper than McM, but I have to factor in MY TIME. IS IT WORTH IT to save $20? Hopefully you're dealing is much larger quantities, but the principles still apply. Find good local suppliers that don't suck up a lot of time to order and deliver reliably (so you don't have to waste time calling and ask where your order is). Also, make strategies. Is it really worth cutting your own material? Should you have parts pre-cut on a laser? Those are commodity services these days. When I need parts laser-cut, I almost never ask for a quote. My local guys are so fast and cheap!
4. Develop a replenishment system for tools so that you never run out of the highly-used items. The last thing you want is "inventory hell" where you have tools laying all over the shop. I don't do much myself, but I just tossed a bunch of misc drill bits and have two full fractional/number/letter indexes and when one wears out, there's a back-up and then I order the new back-up (i.e. I should always have two on-hand). My needs are small, you may need to expand that strategy.
Remember, time is money and there should be more valuable things you can do with it than trying to save a few bucks here and there! Also, the time spent replenishing things you are "out of" is usually worth less than than the time you are losing by not having it (i.e. not making parts!).
Good luck,
The Dude