I've been working on the economic aspect of the game. Tonight I will release a new version after I'm done working out the kinks. What it will feature:
Fixed idle fleet merging bug
Empire Reserves (if you don't spend all of your income, it will go into reserves)
Ability to spend more than you earn if you have reserves left.
Interest rate for reserves, they will earn some money even if there are no money going into it.
What's with the capped spending? When you click on "End Turn", it will check to ensure that you have sufficient income AND reserves for your budget that turn. If you're spending more than you can afford, it will prompt you to adjust your budget. You cannot end turn until the budget is fixed.
While I was working on the economics, I thought of a couple nifty features that I haven't really seen in any other TBS games. Borrowing money with interest rate, and liquidating.
Let's say that you have an ally that's earning a lot of money. You hit a rough patch, and ask your ally to lend you 200 BC, with some interest rate. The 200 BC is directly deposited into your reserve, and you pay your ally back each turn automatically, plus interest. So let's say you take 20 turns to pay back your ally, with some interest rate. So you pay 15 BC per turn, which results in a total payback of 300 BC.
The amount of turns and interest rate will be set automatically, so you just ask for an amount, and the game will handle the rest. Advances in technology will enable you to get a lower interest rate.
Now what happens if you can't pay your ally back? It'd prompt you saying that you can't afford your budget. The best thing to do is to scrap your ships (reducing the upkeep, and getting the scrap money to pay back). If you don't want to scrap ships, or don't have any ships left, then the next option is to sell some of your planets. Each planet will have an "estate value". Newly colonized planets sell for a lot less than a fully developed planet. (Think of Russia selling Alaska to USA)
This will present an interesting twist to the game. An empire gets wiped out because it managed its funding poorly. All of its ships were scrapped, and all of the planets were sold. I don't think I've ever seen a TBS with this kind of defeat. Master of Orion 3 came close, with sections of empire revolting away if the empire is approaching bankruptcy.
In diplomacy, you can trade planets, but each planet will have its estate value listed, so you could trade one of your fully developed planet (worth 400 BC) for four of his planets (worth 395 BC total). Or trade technology for planet, or money.
Back on topic of development, I plan to work on planetary development after the update is released. It will feature a couple of things that you can develop on planets: Factories and Labs. It's not a complicated screen, just that there will be some tedious user interface programming.