I would keep an eye on Cervelli as a mid-season move. Last year of his contract. Will depend on how the Pirates do in the first half.
Most cost effective way to improve the offense: replacing Flaherty (182 PAs in 2018, including 167 against righties against whom he put up a .601 OPS) with a competent backup infielder. But there is a whole thread about that.
And what this all comes back to in the end is that the offensive upgrades have to come in the form of a corner OF and Catcher (and this one certainly may not be cost-effective). I think we'd all much prefer the more prudent cost-effective moves/trades/signings whenever possible, but the most optimal moves may not always be available for AA to make.
Trying to read between the lines a little here, I'm beginning to think that AA wants to improve the team this winter - and be even more competitive next season - but that he may feel like 2020 is when he's going to push all his chips in unless he can pull off a major (and I mean MAJOR) trade this winter. Think about it - with all this money to spend, he continuously tells the press that the fans are going to be disappointed if they're expecting the Braves to add ANY of the top-tier free-agents that are available. We "need" TOR help, but he said don't expect a Corbin signing. We "need" a corner OF upgrade, but don't expect him to be in on Harper. We "need" an offensive upgrade behind the plate, but the main focus there is on defense and framing. While we don't necessarily "need" an upgrade a SS, I can't imagine that Machado wouldn't be a substantial improvement for the team overall in the long run (even with his defensive limitations), yet he has no intention of going there either.
We haven't really looked further ahead other than with prospects, but the market's going to be full of options to fill the holes we would have in 2020 as well. TOR arms? Verlander, Cole, and Wheeler will be free-agents, and Arrieta and Darvish can opt-out after next season. Corner OFs? Khris Davis, Puig, Castellanos, and Ozuna will be free-agents after next season. Arenado and Rendon could be 3B options if they don't sign extensions. By the time next winter rolls around, we could be looking at Pache and Riley as bench options if they're not traded - and we could even see Ender traded to make room for Pache.
For this exercise, I'm going to rule Arenado and Rendon out since it's pretty clear that they seem to be comfortable that Riley or a combination of Riley and Camargo are the answer over there. I agree with those who think the acquisition cost for Realmuto is going to be too high, ESPECIALLY if you're looking at 2020 as the first year you expect to make a deep run with a real chance to win the whole shooting match - and he can walk following that season. The Catcher pool isn't particularly deep next offseason, so Grandal kinda has to become Target #1 this winter - he's a substantial upgrade (both offensively and defensively) and even if it costs a little more than you'd like to spend, Flow and Julio come off the books next winter to help pay for him and he's young enough that you should be able to pair him with Contreras as age becomes more of an issue.
Like a lot of folks I think a big trade may be coming that could seriously enhance our chances in 2019, but I'm beginning to like the idea of AA backing the truck up and unloading a bunch of prospects in Seattle rather than handing them to the Marlins where they could hurt us for years to come. Assuming they choose to rebuild (which I'm still not convinced they'll do), go get Paxton AND Haniger. The only prospects that I'd treat as "off-limits" (to what extent you can) would be Riley, one of Pache or Waters, and Contreras. Don't spend another dime on a free-agent this winter, and do what you can to extend Paxton. Someone else can do the chart machinations, but I'm guessing a Wright/Anderson/Pache/Wilson or Fried/Allard or Wentz plus a couple throw-ins offer might be enough? That would leave you with a rotation of Paxton, Folty, Newk, Gausman, Julio with Touki, Gohara, Soroka, and one or two of Wilson/Fried/Allard in Gwinnett. Newk, Gohara, and Fried or Wilson spend 2019 as SPs to see if one can take the needed step forward, and are shifted to the pen full-time for good if they don't as potential late-inning options.
That would give you Acuna, Albies, Freddie, Haniger, Grandal, Camargo/Riley, Ender, Swanson all controlled through 2021 (or longer) with the flexibility to replace Flowers with A-Jax/Contreras in 2020, Ender with Waters when he's ready, and Gausman, Julio, and Viz when their deals are up.