At first I thought that maintenance costs were a major part of the game. After playing for a while I just find them annoying and would like to find some way to offset them easily. After mulling over several ideas, this is what I came up with: a ship module that produces credits.

While there are many ways this could work, the way I pictured would have a series of quests. The quests would be qualified for by level, not by completing the previous quest. Upon completion, each quest would award a 'License' module that would produce a daily amount of credits appropriate to the expected module cost for the level required to start the quest. This income would be gathered at the same time as maintenance and would lower the maintenance cost displayed.

Postal License: Having determined you meet their requirements, your government has authorized you to carry mail between worlds and pays you X credits daily for this service.

Living Cargo License: Your ship has been authorized to carry livestock between worlds. In order to encourage genetic diversity, the government pays you X credits for this service.

Exotic Environments License: Many organic compounds require specialized storage. As few ships are able to transport such materials, the government is willing to give you X credits daily for having such ability.

Passenger License: The government has realized that your ship is suitable passenger traffic and subsidizes you X credits in order to encourage travel between worlds.

Medical Supplies License: Being suited to safely carry medical supplies, the government awards you X credits daily in exchange for such transportation in an emergency.

Hazardous Material License: Having equipped your holds with special protective and handling measures the government authorizes you to carry hazardous materials and provides tax incentives amounting to X credits daily.

Diplomatic License: Having agreed to keep your ship on call for, and made the required arrangements for, diplomatic transport, the government awards you X credits daily.

Official Secrets License: After a thorough investigation the government has allowed your ship to carry diplomatic, secret, and critical information between worlds. To allow you to maintain the special equipment required for this they award you X credits daily.

just wait untill you get to about rank 80 or so. Then if you dont make sure you have good income, upkeep will destroy you.

These could be a good idea. I like it a lot (even if it added a tiny bit every pay on the clock). But this is totally up to dan and a crew.

But what if it went over your upkeep?

It would be bad in a sense. Someone could get credits without any upkeep/actions = Money maker easily

Need money? Get those miners working hard!
Or just sell your artifacts to needy players. Artifacts are always low in stock, especially those nice ones