You're going to need a lot of money in Arcade Legends. Here are a few tips to help with that.

Complete missions daily.

Sell unneeded items, and make sure to price low enough that potential buyers can't resist. Don't be afraid to sell rare or epic equipment, either, if you have no use for it. You'll amass a fortune more quickly that way and add room in your inventory for stuff that you find more relevant.

Check offers daily, as sometimes you can get free gold or platinum easily and those offers change regularly.

If you trade with someone, pay close attention. Don't accept a trade unless you're certain the items on-screen are the ones you agreed to, and that the funds being offered are also appropriate.