Shells are part of the equation - and sure I'd recommend you reload - like Dave and others advised, you can reload a premium shell, at today's component prices, for about $4 a box ( I'm currently at $3.75 for 1 oz loads in 12ga. ......... $ 3.04 for a 3/4 oz 28ga load ....etc ).
Today's progressive loaders - are very quick / many of them turning out 20 boxes an hour easily - like the MEC 9000HN / or even the Grabber model will give you at least 10 boxes an hour.
The best prices I've seen on lower velocity shells in 1oz - is about $5.50 a box / and I understand you have ammo issues in CA - but the cheapest prices up here around Seattle is to buy them by the case at your local gun club. My club, sells components and case lot shells to members only, and 7/8 oz of 1 oz Rio brand are about $ 55 for a flat of 10 boxes....
I don't think buying shells online is competitive. You'd be better off to partner with someone / go together on a press if you have to / each do your own loads ( so you don't have any liability to your buddy ) ....and load your own - and save a few bucks / or shoot more with the same amount of money.
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The pain issues you're having, in my opinion, are exaggerated by your ammo choice ....and me personally, at 6'5" and 290 lbs, I understand the "Buffalo" mentality - no challenge is too big / I'll try harder - or I'll just knock it down and wear out the opposition.... But shooting high velocity 1 1/8 oz loads in a 12 ga - will wear you down ! It doesn't make any difference how strong or macho you are ... Recoil is cumulative ...it wears you out ....and it hurts your mental game. The mental part of these games are at least as important as the physical part / and if your head isn't in the game ( ouch, my shoulder hurts when gun goes off ...) you will not shoot your best scores. Its a combination of skills and confidence ...that wins in these games / not the guy with the biggest gage / and the most shot in the pattern. Some of the best Skeet shooters in the world / shoot 20ga guns ( with 7/8 oz of shot ) in 12ga events !! They make their living shooting ....and if they thought they could get a 00.0001 % chance of an edge by shooting a 1oz load or a 1 1/8 oz load in a 12ga ...every one of them would make the change ....but they don't ??? They stay with the 20ga ...and win, and win and win ....
But most of the pain issues you're having, in my opinion, are "gun fit" related - and/or fundamental mount issues.
While you're healing - you really need to consider going to a semi-auto / where the action will absorb some of the recoil ....borrow, rent, buy ...whatever .... and it should probably be a gas gun. At the same time - work on fundamentals, Gun Fit, etc ....and let that shoulder heal.
Part of my issue - is the weight of the gun as I've gotten older / and a full shoulder and bicep rebuild on my shooting shoulder. So on days when I'm sore or not feeling as strong - I shoot a 20ga or a 28ga / and a lighter gun around 7 1/2 lbs ---and light loads. Some days I go to my semi-auto / mine happens to be a Benelli super sport ...but whatever you have in a semi auto ...
Somehow we need to convince you, while you can shoot these 1 1/8oz howitzer loads ....it really isn't in your best interst. We all understand, when you miss, its hard not to instinctively reach for a shell with more pellets in it ...( but trust me, it isn't better ... !! ) ....and its abusing your body !! 7/8 oz of shot will break any Skeet or 16 yard Trap target ...in a cloud of dust --- if you center it in the pattern !! The heavier loads / and the lack of fit on your gun ...and the abuse to your body --- are making it worse ..not better. You can stand there ....to use my analogy ....like a "Buffalo" ....( and I often do as well ) ....but when I close my eyes, I know I'm just being stupid ....
