Just throwing an idea here for anyone who have the time to do it.
It'll be awesome if there's an upgrade guide that tells you the best order of upgrades to buy in order to maximize your profits.
Hey, I've been partially doing this for me, however I didn't write the prices down while upgrading my mine. We could collect the upgrade costs here from people with mines at different stages. When there's a comprehensive list I will be happy to make the calculations and post them here.

Or we could ask OP to list the full prices

Edited my previous post
That's kinda what I do, calculate the extra % I'll be getting then divide by the cost. but to be more accurate the time to mine gold for the upgrade should be considered. I think everyone does the simple math, so I was more talking about the more accurate time dependent math.
You are right, time is also a factor to consider. If you are mining manually, i.e. don't buy boosts like the troll, you also have to decide whether and when you invest into chambers and equipment which would give you additional time mining without you continously clicking on ads.
The fastest way to upgrade your mine without buying the boost would be to buy no chambers and equipment at all and continue clicking on ads every 5 minutes, while always upgrading with the best (delta gold)/(price of upgrade) ratio.
I have been playing this game since December last year and been using the troll for a good part of that time.
But even with this advantage it will take at least 4 to 5 months to fully upgrade your mine, imho.