It's all relevant to the campaign. There is no hard and fast "give your players X amount of gold every day"
There's a few things to take into consideration when deciding how much gold your party "needs".
- How much XP you're giving them every day
- What they can spend their money on in your campaign
- What your party plans on doing with their money
- What type and what difficulty of campaign you're going to run
How much XP you're giving them every day
Page 84 of the DMG has an Adventuring Day XP table. A standard campaign, they suggest, should give a party a certain amount of encounter XP per day. It's not so much that they need to hit these numbers every day, but rather what their spells and abilities will be able to handle. At level 1, your party will be able to handle 300 xp per day per character, because they have limited abilities and spell slots. If your characters are having trouble with this, maybe give them more gold to spend. Take this into consideration when determining how much gold they need to keep up with their growth.
What they can spend their money on in your campaign
Your setting will directly influence what your party can spend their money on. If they are far from civilization with nothing to spend the money on, then maybe they don't really need much at all. If they are in a bustling city, trying to get in close with the nobels, they're going to need a lot more to enable a wealthy life style. What are they eating, where are they sleeping, and what are they buying? Does it matter to your party? The DMG is full of information on life style and how much it costs.
What your party plans on doing with their money
Talk to your players about what they want to do in this campaign. I'll say it again: Talk to your players. The types of things your players want to do will directly influence how much gold you're going to throw at them to help (or not) them achieve these goals. If your players want to build a fortress, they're gonna need a way to get a lot of gold. If they don't want to use gold as a big resource, they wont need much at all. For example, in our current campaign we're running a pirate ship. Because we've talked about maybe buying more boats or outfitting our crew, our DM offers us thousands of gold in our quests because we are spending it on our fleet and crew, rather than buying equipment for ourselves. The amount of gold in this example is further reduced by our lack of need for magic items, as we've been outfitted pretty decently in past encounters.
What type and what difficulty of campaign you're going to run
The amount of gold and what they do with it correlates to the dangers they will face in battle and the things your party wants to do. Chapter 7 details treasure hoards for certain levels, and that's a good starting point. If you are unsure of what to give them, use that table as a base line.
The "Starting Equipment" table on page 38 of the DMG gives us a glimpse into a little bit of how the designers distinguish different play-styles. There are 3 collumns: Low Magic Campaign, Standard Campaign, and High Magic Campaign. This table is meant to help you figure out what kind of equipment your characters need for what type of setting. Also, pages 38–41 give you detailed descriptions of the different flavors of fantasy and how they can be played. Certain styles of campaign need less gold than others. Also, your party's level and their enemies influence how much gold they would need for equipment and the like.
Using all this information, you should be able to home in on an appropriate amount. You might not get it right the first time and that's okay. DM-ing is not a science and takes some trial and error.