OP sounds like he has a good idea of what is going on. It's just that his main job isn't thief. That's why he's asking about 'wal-mart' (with a dash of merc) builds.
Really, even if 100% of the other people here, or anywhere for that matter, disagreed with the SA/TA analysis, I'd frown in worry but eventually have to stick by it. I have a lot of confidence in it and it's not 100% fleshed out, but I feel that the parts that aren't fleshed out compensate a bit with each other. It has a very slight bias towards haste so you might be able to downplay it very slightly. There are different values for haste in there, so you can pick the one you like. Also, it is a big deal that sometimes you sa/ta and don't follow up with another attack round (IE you kill the mob, or you run away). I'd say this pretty much balances out with the fact that the math doesn't even incorporate the extra TP you gain from faster attacks. You could also throw in 'missed' SA/TA's, which would obviously favor haste/dw/t.a./d.a. Those small details aside, the formula is pretty good. But it's complicated; if I had to guess on it, I'd say not a single other person has used the formula I posted there for their own purposes, or check its accuracy.
That was a year ago, but the basic principles behind the formula are yet to change (edit: mostly; see #4 below). The only things to look out for would be (1)I haven't updated it to our current knowledge of crit, but this is incredibly miniscule, (2)I haven't updated it for our current knowledge of pDif, which is grossly incomplete--and hey, that's almost ok, because 99% of FFXI calculations for the past years have relied on pDif information that was false (inaccurate) anyway. (3)It would have to be updated to deal with future trends in what we fight, and possible future changes in the game formulae.
(4)It doesn't account for the new crit trait. This is estimated by gobli to be 5%. But I've not seen any samples for this or any others, except for my friend's, which suggests its 10%. Still, hard to doubt gobli. I'd like to see more testing (as if we had lives.
Remedy: If you want, a mock-remedy for this would be to just multiply "spike damage stats" (dex, agi, str, atk) by 1.05 to accommodate a 5% boost from the trait. Not the perfect solution, but easy and better than nothing.
* * *
So for gearing sa/ta, I'd definitely go by my guide. Otherwise, the advice you've gotten here has been pretty good. I'll see what I can add though. Kupo head with 10acc/3haste is great for thieves that are very serious about the job, but if you're not you could just go with turban or the delicious brisk mask. Might have to change my kupo head if/when I get that. There's also the new heads with roughly 15acc/4atk on them, but they're r/ex and hard to get. I'd use your kupo head for multi-hit WS. But of course since thief isn't your main job you might have other uses for that. If you do want to use 3-mini-expansion gear for Thf though, then concerning Mirke I'd go w/ what Meldi said. I'd also get a sharpeye mantle. At this point you may want multiple builds. I mean, idk about other jobs but thief definitely should. Rapp/Forager's vs Sharpeye/Mirke for example. You can also take advantage of feint by using the low-acc build. Even as a non-main thief, you could probably make good use out of carrying Sharpeye, Cuchulain's, /and/ Forager's.
Dusk for hands prolly. I'd say aurore over dusk for feet. But really I'm sure it's a bit close. Merc as much heca and homam as you're willing/want to, really. Well, in the way of homam head and legs and body aren't very useful anymore. Legs and body have their uses. Heca body can be replaced. Heca head can be situationally (rarely? idk)be replaced by kupo head. On Asura, mercing heca head for 2-3m was definitely viable for a long time. But you have to go to Aery and talk to sellers often. For WS feet, might want to consider dragon leggings +1 or the new 6dex/6agi ones; can always try for heca. Might as well get a cuchulain's belt, but I can't really tell you to pick warwolf vs virtuoso. Depends on your WS, what you do, merits, etc. Might as well use sea gorgets for WS. I merced Love Torque for 5m but that looks to be out of your price range.
As far as newer gear, look over the 'best' thread and you should find some things. Like the new Agi neck, which is like 400k on my server atm. Not sure if it's in your price-range given that it's just for TA, but hey, it's wal-mart. Speaking of wal-mart, new rings shouldn't actually be that expensive. I recently bought an AGI ring for 1.8m--biggest financial mistake I've made in the game; dk what I was thinking. I made my second one for about 500k a week later, but of course I have synergy skill and had to look around for goldsmithers to invite to my party. My 6dex ring was only 600k as well, doing the same thing. Barely more than the 5-stat rings (str being one exception).
Ehh, lastly, if you want to know about new gear for SA/TA unstacked, just look at new gear and use the stat-by-stat analysis that I put in the guide. That's what it's there for. And use (#4) above to compensate for some of the stats if you want. Or check the 'best' thread.