Exeggutor

I would finger cross for weather boosted LV35 exercute or eggy, instead of maxing it out. They are very common under sunny/clear.(my city always sunny).
I kinda regret maxing out my previous eggy, But it is OK, since it is still best grass type.

Best grass type for a while. It wont hurt having few of them.

But idk what grass is good for atm.
There is water for ground and rock.
Electric for water.

Grass resisted by 7 types too.

So sad cuz its my fav type too.

There probably isn't enough in gen 3 to spend that much stardust on. Must-haves are Gardevoir, Metagross, possibly Salamence (mostly unnecessary if you have Dragonites already) and some of the legendaries, where rare candy soon becomes more of a limiting factor than dust.

If you don't have a full team against future Groudon/Kyogre raids (Kyogre is Groudon's top counter if it comes out first), Exeggutor pulls double duty there so it's a pretty good investment. Also helps if you want to solo Omastar, although you can easily do that with L30 wild caught grass mons that have grass/SoB (or LB) moveset. Weather boosted L30+ makes it even easier.

With 3 million, you can kind of do both, can't you?