You should combine this with the "Pure Pawn" Trophy. For this trophy you need to have a balance of 30,000 credits at any given time. It's not cumulative. I recommended that you do this on a Rookie playthrough.
To make sure you get it, from the beginning of the game you should horde your items and credits. Thoroughly search the levels as well for credits and items from Lockers and Human corpses. I never bought any upgrades or used any items. By the start of level 4 I had around 25,000 credits saved and the combined selling price of all my items was around 8,000 credits. What to do when you reach a similar situation is first of all save your game. Then when at an Intex Terminal, sell all your items so you have a balance of over 30,000 thousand to achieve "Cash is King". You then have to leave the Intex Terminal for the trophy to pop.
Next, return to the terminal and spend all your money on more items to sell. Which type doesn't matter. The ratio of buying price to selling price is the same for all items. Then sell all of those items and leave the Intex Terminal again. The "Pure Pawn" Trophy should now pop as well. Now just load up your previous save and you will be free to use your items and spend credits on upgrades, etc for the rest of the game. Since it requires you to go for it over most of a playthrough I've put this trophy as missable.