This involves editing a game file. Open your Keeper directory and go into the data sub-directory, in here there is a file called: creature.txt. Disable the read-only function and make a backup before editing. First you will see all stats for your creatures, best not change any of these. Scroll down and you will see a list of all rooms. The second column of numbers is their cost, change this to 0 and in game every room will cost absolutely nothing.

Scroll further down and you will see a list of spells. You can edit all columns besides the first one. For example; MAGIC_CREATE_IMP has a 2 followed by its prices, change every number after this to 0 and you can get an infinite number of imps for nothing.

For a lot of gold scroll further down. You will see GAME_GOLD_PER_GOLD_BLOCK change the second column to a high number such as 9999. Every gold block will give you that amount of money. You can also edit other money related stats.

Important Note: Do NOT edit sections which say "do not change", any other parameter is fine to edit.