This forum thread is very useful :
http://www.gamefaqs.com/boards/genmessage.php?board=926714&topic=45423201
xoxo
hm
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You can do a buy low sell high sort of tactic with spices:

Red spice costs 3k - can be sold for 16k max
Yellow costs 4,5k - can be sold for 18k (maybe more)
Blue costs 5k - can be sold for 26k max
Green costs 10k - can be sold for 50k max
Pink costs 11k - can be sold for 56k max
Purple costs 16l - can be sold for 76k (maybe more)

Also remember you will get money everytime you destroy an enemy ship or city, and still gain money from completing missons, if your not the trading type.
Also, capturing colonies that are already at t3 will be usefull to you. As you won't have to do any work but will have another spice producing colony.
In any case, spice trading, or "flipping" is your best bet to loads and loads of fast cash, just max out planets of each colour and travel around to sell them, don't try to get the very best price, just sell at the first reasonable one. Then go back and repeat. It may be tedious but if you can hold out for a bit then it will stave off your cash needs for quite a while.
Source(s):
http://forum.spore.com/jforum/posts/list/1633.page

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Find ancient artifacts on different planets in the galaxy. That will help you gain more money by trading the artifacts for money with different species, or your own species. That's one of the only ways to make money in space stage.
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In my opinion, the easiest way to make money quickly in the space stage is to terraform several star systems with rare spice (i.e. pink or purple) to T3 and maximize the production rate on each planet (by using the maximum number colonies and factories and spice storage etc.)
Source(s):
Personal Experience

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