This answer probably won't help the OP, but here's how I do things.
Factory ammo~too heavy to ship efficiently if any volume is involved, so as a rule...I only buy it locally. I don't shoot pistols or ARs, so I have no need for high volumes of inconsistent/throw-away ammo being shot at close ranges. It's all those disciplines require. Were that not the case, I'd be taking advantage of sales that Tenda offer, or other sponsors. (=buy enough/free or cheap shipping)
Rimfire~I buy, and buy it often locally. I know which stores have the brands/types I like to play with...so about every month, I use that as an excuse to visit gun shops. That way I can drool over nice guns/scopes...and not leave TOTALLY empty handed. lol
Shotgun~I try to buy target loads (also used for grouse) every time I'm in a gun store, even if I have no clays/grouse planned. When I take my boys out for clays, they really gobble through it. So, @ $7 a box or so, I'll grab a case of 10 boxes..but sometimes maybe just a couple of loose boxes to add to the small pile at home. Even that way, it'll almost guarantee we can shoot to our hearts content, and I'll still have a few hundred rounds at home just in case.
Centerfire~I'm too frugal to target shoot with centerfire ammo, but I mostly hand load for my 2 rifles anyway. My 17 Hornet shoots factory ammo so well that I basically stopped working up loads for it. Will get back on that this fall/winter...as it might be fun to use that for some target shooting. Sure doesn't use much powder!
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As for what the OP is wanting to do (multiple boxes of .243)~I'd find the best price you can from dealers/online sources...then ask your local gun shop if they can match. I think gun shops get lots of inquiries from "tire-kickers"...so the outcome can be very different if you know your local store has it, you have proof of a lower price (link/flyer)...and ask the question with a pile of cash in your hand. As a friend of mine always said; "money talks, bulls**t walks". lol Margins can be low on some items, so I often find it persuasive to pick a time when you need something else (magazine, cleaning supplies, whatever) and grab that at the same time. Stores can be flexible on one item if they know they can get full margins on something else...and actually make the sale.