Needs way better record-keeping - what are my base stats? What multipliers do I have? How is the damage I get calculated? How much toughness do I actually have, anyway? Etc...
Also, the Sharp Legs upgrade needs a major buff. As-is, the interaction with Fury means it actually makes your total damage go down, and fast too. It's literally better not to buy it at all, at least at the first few levels (maybe the later 16+x the first hit makes up for it, but rn I'm hitting way more than 2/4/8 times a jump so boosting the first few isn't worth it in total.)
Please have envoys only have a timer after you dismiss them and load the game, not after you buy them. It makes new runs really annoying to have to wait half an hour to get this one thing to where you can get it, not even mentioning that most of the things you get probably aren't really what you want. Also the 6 min is probably a bit too long.
In addition, as it is lighter and torchlight are pretty much useless. I get that they're so you can have fast progress through early monsters, but when I kill everything up to 200 in one hit just progressing quickly through the first handful isn't all that appealing. And with how slow getting moon lenses is by the time I have enough of them to get to 200 fast I'll be one-hitting up to 400 so nothing will really have changed. I'm going to wait a while either way. They really need a buff so they're more on ghulclot's level, that one would be worth spending a highly limited resource on.
Someone complained about this in chat. So... next update will remove envoy timer, but you still get some time penalty for dismissing. Also, enemy kill area scaling is getting removed, and torchlight / lighter will get substantial buff.
From that point, given that for division a/y + b/y = (a+b)/y you can calculate the price without regard for price changes up to the milestone and then divide, and then see if that's affordable. The only thing this probably wouldn't work right for is the Retail upgrade, as it modifies its own price. (At least, I think it does? I'm pretty sure it should.) But again, you can just calculate things once and then stuff it in a variable and show that until something gets upgraded or changed, update it, show until upgrade/change, etc.
Or I'm completely misinterpreting what the problem is here - in which case, sorry for being presumptuous. Don't mean to offend.
I appreciate your effort to address this, but the cost does shift every frame. Just to calculate the cost of 1 Farm, the modifiers are; Labour(upgrade), Hardwood(garden), Architect(guest), Paperclip(lens), Score(Achievements), and Perk. Garden modifier is; Gardener(guest). Perk modifier is Master(career). Guest modifier are level, infusion, loyalty, and Senate(career). Then most of those modifiers has MAX modifiers. Frankly... it's ridiculous.
Regarding the problem of being unable to calculate bulk costs, why call for() loops every frame? This is an idle game - if nothing changes, then recalculation shouldn't happen. Can't you just have a whole list of variables like LabourDivision (or something) which holds by how much the Labour upgrade divides the cost of buildings, and then if other upgrades mod the cost as well multiply them all together into a TotalBuildingDivision variable, which only gets updated when one of the constituent upgrades updates. As near as I can tell there's nothing that shifts costs from frame-to-frame, so there shouldn't be a need to calculate it frame-to-frame.
The gold bug kinda kept the game balanced :/ Needs price reduction or revolution increases now I think. Now it takes waay too long. I'm managing to keep up with the Forest for now, but next reset...
There's something weird going on at the T/Qa barrier, or I'm just missing something, but I'm pretty sure we're getting an extra order of magnitude or three in there somewhere? My gold says 1.something T/sec, but I get it in Qa's. Also, please change the gold percentage in happiness to be 100+happiness%, without the +, so we immediately get how many times base we're getting, instead of going into weird mental convulsions where we think +100 to +1000 is times ten production (it's times 5.5)
Found a bug: On level 24, if you clear the double-triangle thingie that goes on and off on the lower right, the first one on the line of the most lower-right rhombus, and then undo, it doesn't come back. Not sure if this happens anywhere else, but I do know this doesn't always happen, tested it on level 23.
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Someone complained about this in chat. So... next update will remove envoy timer, but you still get some time penalty for dismissing. Also, enemy kill area scaling is getting removed, and torchlight / lighter will get substantial buff.